diff --git a/lval/environment.c b/lval/environment.c
index 5ebc75f..133b39d 100644
--- a/lval/environment.c
+++ b/lval/environment.c
@@ -6,6 +6,7 @@
 
 lenv* lenv_new(void) {
     lenv* e = (lenv*) malloc(sizeof(lenv));
+    e->par = NULL;
     e->count = 0;
     e->syms = NULL;
     e->vals = NULL;
@@ -23,12 +24,13 @@ void lenv_del(lenv* e) {
 }
 
 lenv* lenv_copy(lenv* e) {
-    lenv* n = malloc(sizeof(lenv));
+    lenv* n = (lenv*) malloc(sizeof(lenv));
+    n->par = e->par;
     n->count = e->count;
-    n->syms = malloc(sizeof(char*) * n->count);
-    n->vals = malloc(sizeof(lval*) * n->count);
+    n->syms = (char**) malloc(sizeof(char*) * n->count);
+    n->vals = (lval**) malloc(sizeof(lval*) * n->count);
     for (int i = 0; i < e->count; i++) {
-        n->syms[i] = malloc(strlen(e->syms[i]) + 1);
+        n->syms[i] = (char*) malloc(strlen(e->syms[i]) + 1);
         strcpy(n->syms[i], e->syms[i]);
         n->vals[i] = lval_copy(e->vals[i]);
     }
@@ -45,7 +47,12 @@ lval* lenv_get(lenv* e, lval* k) {
         }
     }
 
-    // If no symbol found return error
+    // If no symbol found so far, check in parent
+    if (e->par) {
+        return lenv_get(e->par, k);
+    }
+
+    // If no symbol found and no parent, return error
     return lval_err("Unbounded symbol %s", k->sym);
 }
 
@@ -73,16 +80,24 @@ void lenv_put(lenv* e, lval* k, lval* v) {
     strcpy(e->syms[e->count - 1], k->sym);
 }
 
-lval* lval_fun(lbuiltin func) {
-    lval* v = malloc(sizeof(lval));
-    v->type = LVAL_FUN;
-    v->builtin = func;
-    return v;
+void lenv_def(lenv* e, lval* k, lval* v) {
+    // Iterate until e has no parent
+    while (e->par) { e = e->par; }
+
+    // Put the value in e
+    lenv_put(e, k, v);
+}
+
+lval* lval_builtin(lbuiltin func) {
+  lval* v = malloc(sizeof(lval));
+  v->type = LVAL_FUN;
+  v->builtin = func;
+  return v;
 }
 
 void lenv_add_builtin(lenv* e, char* name, lbuiltin func) {
     lval* k = lval_sym(name);
-    lval* v = lval_fun(func);
+    lval* v = lval_builtin(func);
     lenv_put(e, k, v);
     lval_del(k); lval_del(v);
 }
@@ -108,35 +123,11 @@ void lenv_add_builtins(lenv* e) {
     lenv_add_builtin(e, "max", builtin_max);
     
     lenv_add_builtin(e, "def", builtin_def);
+    lenv_add_builtin(e, "=", builtin_put);
     lenv_add_builtin(e, "ls", builtin_ls);
     lenv_add_builtin(e, "\\", builtin_lambda);
 }
 
-lval* builtin_def(lenv* e, lval* a) {
-    LASSERT_TYPE("def", a, 0, LVAL_QEXPR)
-
-    // First argument is the symbol list
-    lval* syms = a->cell[0];
-
-    // Ensure all elements of the first list are symbols
-    for (int i = 0; i < syms->count; i++) {
-        LASSERT(a, syms->cell[i]->type == LVAL_SYM,
-            "Function 'def' cannot define non-symbol")
-    }
-
-    // Check correct number of symbols and values
-    LASSERT(a, syms->count == a->count - 1,
-        "Function 'def' cannot define incorrect number of values to symbols. Left side %i, right side %i", syms->count, a->count - 1)
-
-    // Assign copies of values to symbols
-    for (int i = 0; i < syms->count; i++) {
-        lenv_put(e, syms->cell[i], a->cell[i + 1]);
-    }
-
-    lval_del(a);
-    return lval_sexpr();
-}
-
 lval* builtin_ls(lenv* e, lval* a) {
     LASSERT_NUM("ls", a, 0)
 
@@ -184,4 +175,90 @@ lval* builtin_lambda(lenv* e, lval* a) {
     lval_del(a);
 
     return lval_lambda(formals, body);
+}
+
+lval* builtin_var(lenv* e, lval* a, char* func) {
+    LASSERT_TYPE(func, a, 0, LVAL_QEXPR)
+
+    lval* syms = a->cell[0];
+    for (int i = 0; i < syms->count; i++) {
+        LASSERT(a, (syms->cell[i]->type == LVAL_SYM),
+            "Function '%s' cannot define non-symbol. "
+            "Got %s, Expected %s.", func,
+            ltype_name(syms->cell[i]->type),
+            ltype_name(LVAL_SYM))
+    }
+
+    LASSERT(a, (syms->count == a->count-1),
+        "Function '%s' passed too many arguments for symbols. "
+        "Got %i, Expected %i.", func, syms->count, a->count-1)
+
+    for (int i = 0; i < syms->count; i++) {
+        // If 'def' define it globally
+        if (strcmp(func, "def") == 0) {
+            lenv_def(e, syms->cell[i], a->cell[i + 1]);
+        }
+        // If 'put' define it locally
+        if (strcmp(func, "=") == 0) {
+            lenv_put(e, syms->cell[i], a->cell[i + 1]);
+        }
+    }
+
+    lval_del(a);
+    return lval_sexpr();
+}
+
+lval* builtin_def(lenv* e, lval* a) {
+    return builtin_var(e, a, "def");
+}
+lval* builtin_put(lenv* e, lval* a) {
+    return builtin_var(e, a, "=");
+}
+
+lval* lval_call(lenv* e, lval* f, lval* a) {
+    // If builtin simply apply that
+    if (f->builtin) { return f->builtin(e, a); }
+
+    // Record argument counts
+    int given = a->count;
+    int total = f->formals->count;
+
+    // // While arguments still remain to be processed
+    while (a->count) {
+        // If we've run out of formal arguments..
+        if (f->formals->count == 0) {
+            lval_del(a); 
+            return lval_err("Function passed too many arguments. "
+                "Got %i, Expected %i.", given, total);
+        }
+
+        // Pop the first symbol from the formals 
+        lval* sym = lval_pop(f->formals, 0);
+
+        // Pop the next argument from the list
+        lval* val = lval_pop(a, 0);
+
+        // Bind a copy into the function's environment
+        lenv_put(f->env, sym, val);
+
+        // Delete the symbol and value
+        lval_del(sym); lval_del(val);
+    }
+
+    // The argument list is now bounded so we can clean up the given
+    lval_del(a);
+
+    // If all formals have been bounded evaluate
+    if (f->formals->count == 0) {
+        // Set environment parent to evaluation environment
+        f->env->par = e;
+
+        // Evaluate and return
+        return builtin_eval(
+            f->env, lval_add(lval_sexpr(), lval_copy(f->body)));
+    } else {
+        // Otherwise return partially evaluated function
+        return lval_copy(f);
+    }
+    return lval_sexpr();
 }
\ No newline at end of file
diff --git a/lval/environment.h b/lval/environment.h
index 815ecbe..816cf8c 100644
--- a/lval/environment.h
+++ b/lval/environment.h
@@ -3,6 +3,8 @@
 #include "base.h"
 
 struct lenv {
+    // Represents the parent environment
+    lenv* par;
     int count;
     char** syms;
     lval** vals;
@@ -10,13 +12,16 @@ struct lenv {
 
 lenv* lenv_new(void);
 void lenv_del(lenv* e);
+lenv* lenv_copy(lenv* e);
+
 // Obtain a variable from the environment
 // e is the environment
 // k is the symbol
 lval* lenv_get(lenv* e, lval* k);
 void lenv_put(lenv* e, lval* k, lval* v);
+void lenv_def(lenv* e, lval* k, lval* v);
 
-lval* lval_fun(lbuiltin func);
+lval* lval_builtin(lbuiltin func);
 
 void lenv_add_builtin(lenv* e, char* name, lbuiltin func);
 void lenv_add_builtins(lenv* e);
@@ -24,6 +29,10 @@ void lenv_add_builtins(lenv* e);
 lval* builtin_def(lenv* e, lval* a);
 lval* builtin_ls(lenv* e, lval* a);
 lval* builtin_lambda(lenv* e, lval* a);
+lval* builtin_def(lenv* e, lval* a);
+lval* builtin_put(lenv* e, lval* a);
+lval* builtin_var(lenv* e, lval* a, char* func);
 
+lval* lval_call(lenv* e, lval* f, lval* a);
 
 #endif
diff --git a/lval/expressions.c b/lval/expressions.c
index e22f101..a84d2de 100644
--- a/lval/expressions.c
+++ b/lval/expressions.c
@@ -3,6 +3,7 @@
 #include <stdlib.h>
 
 #include "expressions.h"
+#include "environment.h"
 #include "numbers.h"
 #include "operations.h"
 #include "error.h"
@@ -85,17 +86,20 @@ lval* lval_eval_sexpr(lenv* e, lval* v) {
 	if (v->count == 0) { return v; }
 
 	// Single expression
-	if (v->count == 1) { return lval_take(v, 0); }
+	if (v->count == 1) { return lval_eval(e, lval_take(v, 0)); }
 
 	// Ensure first element is a symbol otherwise
 	lval* f = lval_pop(v, 0);
 	if (f->type != LVAL_FUN) {
+		lval* err = lval_err(
+			"S-Experssion starts with incorrect type. "
+			"Got %s, Expected %s.",
+			ltype_name(f->type), ltype_name(LVAL_FUN));
 		lval_del(f); lval_del(v);
-		return lval_err("S-expression does not start with function");
+		return err;
 	}
-
 	// If so call the function and return result
-	lval* result = f->builtin(e, v);
+	lval* result = lval_call(e, f, v);
 	lval_del(f);
 	return result;
 }
diff --git a/lval/operations.c b/lval/operations.c
index 0e6e3f6..631054c 100644
--- a/lval/operations.c
+++ b/lval/operations.c
@@ -3,6 +3,7 @@
 #include "numbers.h"
 #include "expressions.h"
 #include "operations.h"
+#include "environment.h"
 
 lval* builtin_op(lenv* e, lval* v, char* sym);