diff --git a/golox/internal/runner/scanner.go b/golox/internal/runner/scanner.go
index fff253d..646c042 100644
--- a/golox/internal/runner/scanner.go
+++ b/golox/internal/runner/scanner.go
@@ -108,6 +108,10 @@ func (s *Scanner) scanToken() {
 			s.scanNumber()
 			return
 		}
+		if isIdentAlpha(c) {
+			s.scanIdentifier()
+			return
+		}
 		lerrors.EmitError(s.line, "Unexpected character.")
 	}
 }
@@ -201,6 +205,18 @@ func (s *Scanner) scanNumber() {
 	)
 }
 
+func (s *Scanner) scanIdentifier() {
+	for isIdentAlphaNumeric(s.peek()) {
+		s.advance()
+	}
+	l := s.source[s.start:s.current]
+	typ := IDENT
+	if kTyp, ok := KeywordTypes[l]; ok {
+		typ = kTyp
+	}
+	s.addToken(typ)
+}
+
 // addToken produces a single token without a literal value.
 func (s *Scanner) addToken(typ TokenType) {
 	s.addTokenWithLiteral(typ, nil)
diff --git a/golox/internal/runner/scanner_const.go b/golox/internal/runner/scanner_const.go
new file mode 100644
index 0000000..aa94484
--- /dev/null
+++ b/golox/internal/runner/scanner_const.go
@@ -0,0 +1,20 @@
+package runner
+
+var KeywordTypes = map[string]TokenType{
+	"and":    AND,
+	"class":  CLASS,
+	"else":   ELSE,
+	"false":  FALSE,
+	"for":    FOR,
+	"fun":    FUN,
+	"if":     IF,
+	"nil":    NIL,
+	"or":     OR,
+	"print":  PRINT,
+	"return": RETURN,
+	"super":  SUPER,
+	"this":   THIS,
+	"true":   TRUE,
+	"var":    VAR,
+	"while":  WHILE,
+}
diff --git a/golox/internal/runner/scanner_util.go b/golox/internal/runner/scanner_util.go
index a9e6eac..a7b7731 100644
--- a/golox/internal/runner/scanner_util.go
+++ b/golox/internal/runner/scanner_util.go
@@ -1,5 +1,15 @@
 package runner
 
+func isIdentAlphaNumeric(c byte) bool {
+	return isIdentAlpha(c) || isDigit(c)
+}
+
+func isIdentAlpha(c byte) bool {
+	return (c >= 'a' && c <= 'z') ||
+		(c >= 'A' && c <= 'Z') ||
+		c == '_'
+}
+
 func isDigit(c byte) bool {
 	return c >= '0' && c <= '9'
 }