diff --git a/Upsilon/Evaluator/Evaluator.cs b/Upsilon/Evaluator/Evaluator.cs
index bda0ad7..20443d4 100644
--- a/Upsilon/Evaluator/Evaluator.cs
+++ b/Upsilon/Evaluator/Evaluator.cs
@@ -3,19 +3,28 @@ using Upsilon.Parser;
 
 namespace Upsilon.Evaluator
 {
-    public static class Evaluator
+    public class Evaluator
     {
-        public static object Evaluate(this ScriptSyntax e)
+        public Script Script { get; }
+        public VariableScope Scope { get; }
+
+        public Evaluator(Script script, VariableScope scope)
+        {
+            Script = script;
+            Scope = scope;
+        }
+
+        public object Evaluate(ScriptSyntax e)
         {
             return EvaluateExpression(e.Statement);
         }
 
-        public static object Evaluate(this ExpressionSyntax e)
+        public object Evaluate(ExpressionSyntax e)
         {
             return EvaluateExpression(e);
         }
 
-        private static object EvaluateExpression(ExpressionSyntax e)
+        private object EvaluateExpression(ExpressionSyntax e)
         {
             switch (e.Kind)
             {
@@ -26,13 +35,17 @@ namespace Upsilon.Evaluator
                 case SyntaxKind.LiteralExpression:
                     return ((LiteralExpressionSyntax) e).Value;
                 case SyntaxKind.ParenthesizedExpression:
-                    return ((ParenthesizedExpressionSyntax) e).Expression.Evaluate();
+                    return Evaluate(((ParenthesizedExpressionSyntax)e).Expression);
+                case SyntaxKind.AssignmentExpression:
+                    return EvaluateAssignmentExpression((AssignmentExpressionSyntax)e);
+                case SyntaxKind.VariableExpression:
+                    return EvaluateVariableExpression((VariableExpressionSyntax) e);
                 default:
                     throw new Exception("Invalid expression: " + e.Kind);
             }
         }
 
-        private static object EvaluateUnaryExpression(UnaryExpressionSyntax e)
+        private object EvaluateUnaryExpression(UnaryExpressionSyntax e)
         {
             var operand  = EvaluateExpression(e.Expression);
             switch (e.Operator.Kind)
@@ -48,7 +61,7 @@ namespace Upsilon.Evaluator
             }
         }
 
-        private static object EvaluateBinaryExpression(BinaryExpressionSyntax e)
+        private object EvaluateBinaryExpression(BinaryExpressionSyntax e)
         {
             var left  = EvaluateExpression(e.Left);
             var right = EvaluateExpression(e.Right);
@@ -75,5 +88,30 @@ namespace Upsilon.Evaluator
             }
         }
 
+        private object EvaluateAssignmentExpression(AssignmentExpressionSyntax e)
+        {
+            var variableName = e.Identifier.Name;
+            var val = EvaluateExpression(e.Expression);
+            if (e.LocalToken == null)
+            {
+                Scope.SetGlobalVariable(variableName, val);
+            }
+            else
+            {
+                Scope.SetVariable(variableName, val);
+            }
+            return val;
+        }
+
+        private object EvaluateVariableExpression(VariableExpressionSyntax e)
+        {
+            var varName = e.Identifier.Name;
+            if (Scope.TryGetVariable(varName, out var value))
+            {
+                return value;
+            }
+            throw new Exception("Unknown variable: " + varName);
+        }
+
     }
 }
\ No newline at end of file
diff --git a/Upsilon/Evaluator/Script.cs b/Upsilon/Evaluator/Script.cs
new file mode 100644
index 0000000..f1e333a
--- /dev/null
+++ b/Upsilon/Evaluator/Script.cs
@@ -0,0 +1,37 @@
+using System.Collections.Generic;
+using Upsilon.Parser;
+
+namespace Upsilon.Evaluator
+{
+    public class Script : VariableScope
+    {
+        private string ScriptString { get; }
+        private Evaluator Evaluator { get; }
+        public readonly ScriptSyntax Parsed;
+
+        public Script(string scriptString)
+        {
+            ScriptString = scriptString;
+            Evaluator = new Evaluator(this, this);
+            Parsed = Parser.Parser.Parse(scriptString);
+        }
+
+        public Script(string scriptString, Dictionary<string, object> variables = null)
+        :base(variables: variables)
+        {
+            ScriptString = scriptString;
+            Evaluator    = new Evaluator(this, this);
+            Parsed      = Parser.Parser.Parse(scriptString);
+        }
+
+        public object Evaluate()
+        {
+            return Evaluator.Evaluate(Parsed);
+        }
+
+        public T Evaluate<T>()
+        {
+            return (T)Evaluator.Evaluate(Parsed);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Upsilon/Evaluator/VariableScope.cs b/Upsilon/Evaluator/VariableScope.cs
new file mode 100644
index 0000000..88595f7
--- /dev/null
+++ b/Upsilon/Evaluator/VariableScope.cs
@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+
+namespace Upsilon.Evaluator
+{
+    public class VariableScope
+    {
+        private VariableScope _parentScope;
+        public readonly Dictionary<string, object> Variables = new Dictionary<string, object>();
+
+        public VariableScope(VariableScope parentScope = null, Dictionary<string, object> variables = null)
+        {
+            _parentScope = parentScope;
+            if (variables != null)
+                Variables = variables;
+        }
+
+
+        public void SetVariable(string key, object value)
+        {
+            if (Variables.ContainsKey(key))
+                Variables[key] = value;
+            else
+                Variables.Add(key, value);
+        }
+
+        public void SetGlobalVariable(string key, object value)
+        {
+            if (_parentScope == null)
+            {
+                SetVariable(key, value);
+            }
+            else
+            {
+                _parentScope.SetGlobalVariable(key, value);
+            }
+        }
+
+
+        public bool TryGetVariable(string key, out object result)
+        {
+            if (Variables.TryGetValue(key, out result))
+            {
+                return true;
+            }
+            if (_parentScope != null)
+            {
+                return _parentScope.TryGetVariable(key, out result);
+            }
+            throw new Exception("Variable not found: " + key);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Upsilon/Parser/ExpressionSyntax/AssignmentExpressionSyntax.cs b/Upsilon/Parser/ExpressionSyntax/AssignmentExpressionSyntax.cs
new file mode 100644
index 0000000..f0d67bc
--- /dev/null
+++ b/Upsilon/Parser/ExpressionSyntax/AssignmentExpressionSyntax.cs
@@ -0,0 +1,29 @@
+using System.Collections.Generic;
+
+namespace Upsilon.Parser
+{
+    public class AssignmentExpressionSyntax : ExpressionSyntax
+    {
+        public AssignmentExpressionSyntax(SyntaxToken localToken, IdentifierToken identifier, SyntaxToken equalsToken,
+            ExpressionSyntax expression)
+        {
+            LocalToken = localToken;
+            Identifier  = identifier;
+            EqualsToken = equalsToken;
+            Expression  = expression;
+        }
+
+        public override SyntaxKind Kind => SyntaxKind.AssignmentExpression;
+
+        public SyntaxToken LocalToken { get; }
+        public IdentifierToken      Identifier { get; }
+        public SyntaxToken EqualsToken { get; }
+        public ExpressionSyntax Expression { get; }
+
+        public override IEnumerable<SyntaxNode> ChildNodes()
+        {
+            yield return Identifier;
+            yield return Expression;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Upsilon/Parser/ExpressionSyntax/VariableExpressionSyntax.cs b/Upsilon/Parser/ExpressionSyntax/VariableExpressionSyntax.cs
new file mode 100644
index 0000000..2e1e401
--- /dev/null
+++ b/Upsilon/Parser/ExpressionSyntax/VariableExpressionSyntax.cs
@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+
+namespace Upsilon.Parser
+{
+    public class VariableExpressionSyntax : ExpressionSyntax
+    {
+        public IdentifierToken Identifier { get; }
+
+        public VariableExpressionSyntax(IdentifierToken identifier)
+        {
+            Identifier = identifier;
+        }
+
+        public override SyntaxKind Kind => SyntaxKind.VariableExpression;
+        public override IEnumerable<SyntaxNode> ChildNodes()
+        {
+            yield return Identifier;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Upsilon/Parser/IdentifierToken.cs b/Upsilon/Parser/IdentifierToken.cs
new file mode 100644
index 0000000..7e306c9
--- /dev/null
+++ b/Upsilon/Parser/IdentifierToken.cs
@@ -0,0 +1,19 @@
+using System.Collections.Generic;
+
+namespace Upsilon.Parser
+{
+    public class IdentifierToken : SyntaxToken
+    {
+        public IdentifierToken(string name, int position, int length) : base(SyntaxKind.Identifier, position, name, null)
+        {
+            Name = name;
+        }
+
+        public string Name { get; }
+        public override SyntaxKind Kind => SyntaxKind.Identifier;
+        public override IEnumerable<SyntaxNode> ChildNodes()
+        {
+            yield break;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Upsilon/Parser/Lexer.cs b/Upsilon/Parser/Lexer.cs
index 2fa89c1..8f9c73b 100644
--- a/Upsilon/Parser/Lexer.cs
+++ b/Upsilon/Parser/Lexer.cs
@@ -127,16 +127,21 @@ namespace Upsilon.Parser
         private SyntaxToken LexIdentifierOrKeyword()
         {
             var start = _position;
-            var numStr = new StringBuilder();
-            numStr.Append(Current);
+            var stringBuilder = new StringBuilder();
+            stringBuilder.Append(Current);
             while (char.IsLetterOrDigit(Next) || Next == '_')
             {
-                numStr.Append(Next);
+                stringBuilder.Append(Next);
                 _position++;
             }
 
-            var kind = SyntaxKeyWords.GetSyntaxKind(numStr.ToString());
-            return new SyntaxToken(kind, start, numStr.ToString(), null);
+            var kind = SyntaxKeyWords.GetSyntaxKind(stringBuilder.ToString());
+            var str = stringBuilder.ToString();
+            if (kind == SyntaxKind.Identifier)
+            {
+                return new IdentifierToken(str, start, str.Length);
+            }
+            return new SyntaxToken(kind, start, str, null);
         }
     }
 }
\ No newline at end of file
diff --git a/Upsilon/Parser/Parser.cs b/Upsilon/Parser/Parser.cs
index 9e4b828..2c6c561 100644
--- a/Upsilon/Parser/Parser.cs
+++ b/Upsilon/Parser/Parser.cs
@@ -53,9 +53,30 @@ namespace Upsilon.Parser
 
         public ExpressionSyntax ParseExpression()
         {
+            if (Current.Kind == SyntaxKind.Identifier && Next.Kind == SyntaxKind.Equals)
+            {
+                return AssignmentExpression();
+            }
+            if (Current.Kind == SyntaxKind.LocalKeyword && Next.Kind == SyntaxKind.Identifier)
+            {
+                return AssignmentExpression();
+            }
             return ParseBinaryExpression();
         }
 
+        private AssignmentExpressionSyntax AssignmentExpression()
+        {
+            SyntaxToken localKeyword = null;
+            if (Current.Kind == SyntaxKind.LocalKeyword)
+            {
+                localKeyword = MatchToken(SyntaxKind.LocalKeyword);
+            }
+            var identifier = (IdentifierToken)MatchToken(SyntaxKind.Identifier);
+            var assignmentToken = MatchToken(SyntaxKind.Equals);
+            var expression = ParseExpression();
+            return new AssignmentExpressionSyntax(localKeyword, identifier, assignmentToken, expression);
+        }
+
         private ExpressionSyntax ParseBinaryExpression(SyntaxKindPrecedence.Precedence parentPrecedence = SyntaxKindPrecedence.Precedence.None)
         {
             ExpressionSyntax left;
@@ -96,6 +117,9 @@ namespace Upsilon.Parser
                 case SyntaxKind.TrueKeyword:
                 case SyntaxKind.FalseKeyword:
                     return ParseBoolean();
+                case SyntaxKind.Identifier:
+                    var token = MatchToken(SyntaxKind.Identifier);
+                    return new VariableExpressionSyntax((IdentifierToken) token);
                 default:
                     throw new Exception("Unknown primary expression type: " + Current.Kind);
             }
diff --git a/Upsilon/Parser/SyntaxKeyWords.cs b/Upsilon/Parser/SyntaxKeyWords.cs
index b23c933..987a629 100644
--- a/Upsilon/Parser/SyntaxKeyWords.cs
+++ b/Upsilon/Parser/SyntaxKeyWords.cs
@@ -16,6 +16,8 @@ namespace Upsilon.Parser
                     return SyntaxKind.AndKeyword;
                 case "or":
                     return SyntaxKind.OrKeyword;
+                case "local":
+                    return SyntaxKind.LocalKeyword;
                 default:
                     return SyntaxKind.Identifier;
             }
diff --git a/Upsilon/Parser/SyntaxKind.cs b/Upsilon/Parser/SyntaxKind.cs
index cf016f3..a3bb0f3 100644
--- a/Upsilon/Parser/SyntaxKind.cs
+++ b/Upsilon/Parser/SyntaxKind.cs
@@ -24,6 +24,7 @@ namespace Upsilon.Parser
         NotKeyword,
         AndKeyword,
         OrKeyword,
+        LocalKeyword,
 
         Identifier,
 
@@ -32,6 +33,8 @@ namespace Upsilon.Parser
         BinaryExpression,
         LiteralExpression,
         ParenthesizedExpression,
+        AssignmentExpression,
+        VariableExpression,
 
         // script unit
         ScriptUnit,
diff --git a/Upsilon/Parser/SyntaxKindPrecedence.cs b/Upsilon/Parser/SyntaxKindPrecedence.cs
index d323f7b..9074166 100644
--- a/Upsilon/Parser/SyntaxKindPrecedence.cs
+++ b/Upsilon/Parser/SyntaxKindPrecedence.cs
@@ -30,17 +30,23 @@ namespace Upsilon.Parser
         {
             switch (kind)
             {
+                // equality operators
                 case SyntaxKind.EqualsEquals:
                     return Precedence.Equality;
                 case SyntaxKind.TildeEquals:
                     return Precedence.Equality;
+
+                // logical operators
                 case SyntaxKind.AndKeyword:
                     return Precedence.And;
                 case SyntaxKind.OrKeyword:
                     return Precedence.Or;
+
+                // math operators
                 case SyntaxKind.Plus:
                 case SyntaxKind.Minus:
                     return Precedence.PlusMinus;
+
                 case SyntaxKind.Star:
                 case SyntaxKind.Slash:
                     return Precedence.StarSlash;
diff --git a/Upsilon/Parser/SyntaxToken.cs b/Upsilon/Parser/SyntaxToken.cs
index b676a72..f350dfd 100644
--- a/Upsilon/Parser/SyntaxToken.cs
+++ b/Upsilon/Parser/SyntaxToken.cs
@@ -3,7 +3,7 @@ using Upsilon.Text;
 
 namespace Upsilon.Parser
 {
-    public sealed class SyntaxToken : SyntaxNode
+    public class SyntaxToken : SyntaxNode
     {
         public SyntaxToken(SyntaxKind kind, int position, string text, object value)
         {
diff --git a/Upsilon/Utilities/NodeStringFormatter.cs b/Upsilon/Utilities/NodeStringFormatter.cs
index da6be95..0c26e99 100644
--- a/Upsilon/Utilities/NodeStringFormatter.cs
+++ b/Upsilon/Utilities/NodeStringFormatter.cs
@@ -16,6 +16,10 @@ namespace Upsilon.Utilities
                 sb.Append("|-- ");
             }
             sb.Append(token.Kind);
+            if (token is SyntaxToken node && node.Value != null)
+            {
+                sb.Append($" - {node.Value}");
+            }
             foreach (var syntaxNode in token.ChildNodes())
             {
                 sb.Append("\n");
diff --git a/UpsilonTests/BasicMathExpressions.cs b/UpsilonTests/BasicMathExpressions.cs
index a8fc6ea..e9ed4a5 100644
--- a/UpsilonTests/BasicMathExpressions.cs
+++ b/UpsilonTests/BasicMathExpressions.cs
@@ -16,7 +16,7 @@ namespace UpsilonTests
         [InlineData("0.005 + 2.2", 2.205)]
         public void Addition(string input, double expectedOutput)
         {
-            var actual = (double)Parser.Parse(input).Evaluate();
+            var actual = new Script(input).Evaluate<double>();
             Assert.Equal(expectedOutput, actual, 8);
         }
 
@@ -29,7 +29,7 @@ namespace UpsilonTests
         [InlineData("10.256-2.8546", 7.4014)]
         public void Subtraction(string input, double expectedOutput)
         {
-            var actual = (double)Parser.Parse(input).Evaluate();
+            var actual = new Script(input).Evaluate<double>();
             Assert.Equal(expectedOutput, actual, 8);
         }
 
@@ -39,7 +39,7 @@ namespace UpsilonTests
         [InlineData("21312 * 41684", 888369408)]
         public void Multiplication(string input, double expectedOutput)
         {
-            var actual = (double)Parser.Parse(input).Evaluate();
+            var actual = new Script(input).Evaluate<double>();
             Assert.Equal(expectedOutput, actual, 8);
         }
 
@@ -49,7 +49,7 @@ namespace UpsilonTests
         [InlineData("656486 / 5146", 127.57209483)]
         public void Divison(string input, double expectedOutput)
         {
-            var actual = (double)Parser.Parse(input).Evaluate();
+            var actual = new Script(input).Evaluate<double>();
             Assert.Equal(expectedOutput, actual, 8);
         }
 
diff --git a/UpsilonTests/MathPrecedence.cs b/UpsilonTests/MathPrecedence.cs
index 716c720..32b970d 100644
--- a/UpsilonTests/MathPrecedence.cs
+++ b/UpsilonTests/MathPrecedence.cs
@@ -11,7 +11,7 @@ namespace UpsilonTests
         [InlineData("(10 + 5) * 5", 75)]
         public void Parenthesis(string input, double expectedOutput)
         {
-            var actual = (double)Parser.Parse(input).Evaluate();
+            var actual = new Script(input).Evaluate<double>();
             Assert.Equal(expectedOutput, actual, 8);
         }
 
@@ -20,7 +20,7 @@ namespace UpsilonTests
         [InlineData("5 + 10 * 5", 55)]
         public void MultiplicationBeforeAddition(string input, double expectedOutput)
         {
-            var actual = (double)Parser.Parse(input).Evaluate();
+            var actual = new Script(input).Evaluate<double>();
             Assert.Equal(expectedOutput, actual, 8);
         }
 
diff --git a/Yc/Program.cs b/Yc/Program.cs
index 8679282..2f958f3 100644
--- a/Yc/Program.cs
+++ b/Yc/Program.cs
@@ -1,6 +1,7 @@
 using System;
+using System.Collections.Generic;
 using Upsilon.Evaluator;
-using Upsilon.Parser;
+using Upsilon.Utilities;
 
 namespace Yc
 {
@@ -9,6 +10,7 @@ namespace Yc
         static void Main(string[] args)
         {
             Console.WriteLine("Upsilon REPL");
+            Dictionary<string, object> variables = new Dictionary<string, object>();
             while (true)
             {
                 Console.Write("» ");
@@ -18,9 +20,10 @@ namespace Yc
                     return;
                 }
 
-                var parser = Parser.Parse(input);
-                //Console.WriteLine(parser.Print());
-                Console.WriteLine(parser.Evaluate());
+                var parsed = new Script(input, variables);
+                //Console.WriteLine(parsed.Parsed.Print());
+                Console.WriteLine(parsed.Evaluate());
+                variables = parsed.Variables;
             }
         }
     }