diff --git a/src/build/compile_test.rs b/src/build/compile_test.rs
index 8db95d8..92dbaa4 100644
--- a/src/build/compile_test.rs
+++ b/src/build/compile_test.rs
@@ -1,7 +1,8 @@
 use super::{Builder, Val};
+use std;
 
 fn assert_build<S: Into<String>>(input: S, assert: &str) {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.build_file_string(input.into()).unwrap();
     let result = b.eval_string(assert).unwrap();
     if let &Val::Boolean(ok) = result.as_ref() {
diff --git a/src/build/mod.rs b/src/build/mod.rs
index 7a33b84..bf7e91a 100644
--- a/src/build/mod.rs
+++ b/src/build/mod.rs
@@ -23,7 +23,9 @@ use std::fmt::{Display, Formatter};
 use std::fs::File;
 use std::io::Read;
 use std::ops::Deref;
+use std::path::PathBuf;
 use std::rc::Rc;
+use std::string::ToString;
 
 use ast::*;
 use error;
@@ -35,6 +37,8 @@ impl MacroDef {
     /// Expands a ucg Macro using the given arguments into a new Tuple.
     pub fn eval(
         &self,
+        root: PathBuf,
+        env: Rc<Val>,
         mut args: Vec<Rc<Val>>,
     ) -> Result<Vec<(Positioned<String>, Rc<Val>)>, Box<Error>> {
         // Error conditions. If the args don't match the length and types of the argdefs then this is
@@ -54,7 +58,7 @@ impl MacroDef {
         for (i, arg) in args.drain(0..).enumerate() {
             scope.entry(self.argdefs[i].clone()).or_insert(arg.clone());
         }
-        let b = Builder::new_with_scope(scope);
+        let b = Builder::new_with_env_and_scope(root, scope, env);
         let mut result: Vec<(Positioned<String>, Rc<Val>)> = Vec::new();
         for &(ref key, ref expr) in self.fields.iter() {
             // We clone the expressions here because this macro may be consumed
@@ -272,6 +276,7 @@ type ValueMap = HashMap<Positioned<String>, Rc<Val>>;
 
 /// Handles building ucg code.
 pub struct Builder {
+    root: PathBuf,
     env: Rc<Val>,
     /// assets are other parsed files from import statements. They
     /// are keyed by the normalized import path. This acts as a cache
@@ -344,21 +349,26 @@ impl Builder {
     }
 
     /// Constructs a new Builder.
-    pub fn new() -> Self {
-        Self::new_with_scope(HashMap::new())
+    pub fn new<P: Into<PathBuf>>(root: P) -> Self {
+        Self::new_with_scope(root, HashMap::new())
     }
 
     /// Constructs a new Builder with a provided scope.
-    pub fn new_with_scope(scope: ValueMap) -> Self {
+    pub fn new_with_scope<P: Into<PathBuf>>(root: P, scope: ValueMap) -> Self {
         let env_vars: Vec<(Positioned<String>, Rc<Val>)> = env::vars()
             .map(|t| (Positioned::new(t.0, 0, 0), Rc::new(t.1.into())))
             .collect();
-        Self::new_with_env_and_scope(scope, Val::Tuple(env_vars))
+        Self::new_with_env_and_scope(root, scope, Rc::new(Val::Tuple(env_vars)))
     }
 
-    pub fn new_with_env_and_scope(scope: ValueMap, env: Val) -> Self {
+    pub fn new_with_env_and_scope<P: Into<PathBuf>>(
+        root: P,
+        scope: ValueMap,
+        env: Rc<Val>,
+    ) -> Self {
         Builder {
-            env: Rc::new(env),
+            root: root.into(),
+            env: env,
             assets: HashMap::new(),
             files: HashSet::new(),
             out: scope,
@@ -416,10 +426,13 @@ impl Builder {
     fn build_import(&mut self, def: &ImportDef) -> Result<Rc<Val>, Box<Error>> {
         let sym = &def.name;
         let positioned_sym = sym.into();
-        if !self.files.contains(&def.path.fragment) {
+        let mut normalized = self.root.to_path_buf();
+        normalized.push(&def.path.fragment);
+        let key = normalized.to_str().unwrap().to_string();
+        if !self.files.contains(&key) {
             // Only parse the file once on import.
             if self.assets.get(&positioned_sym).is_none() {
-                let mut b = Self::new();
+                let mut b = Self::new(normalized);
                 try!(b.build_file(&def.path.fragment));
                 let fields: Vec<(Positioned<String>, Rc<Val>)> = b.out.drain().collect();
                 let result = Rc::new(Val::Tuple(fields));
@@ -985,7 +998,7 @@ impl Builder {
             for arg in args.iter() {
                 argvals.push(try!(self.eval_expr(arg)));
             }
-            let fields = try!(m.eval(argvals));
+            let fields = try!(m.eval(self.root.clone(), self.env.clone(), argvals));
             return Ok(Rc::new(Val::Tuple(fields)));
         }
         Err(Box::new(error::Error::new(
@@ -1048,7 +1061,7 @@ impl Builder {
             let mut out = Vec::new();
             for expr in l.iter() {
                 let argvals = vec![try!(self.eval_expr(expr))];
-                let fields = try!(macdef.eval(argvals));
+                let fields = try!(macdef.eval(self.root.clone(), self.env.clone(), argvals));
                 if let Some(v) = Self::find_in_fieldlist(&def.field, &fields) {
                     match def.typ {
                         ListOpType::Map => {
diff --git a/src/build/test.rs b/src/build/test.rs
index b316ef4..8fa028e 100644
--- a/src/build/test.rs
+++ b/src/build/test.rs
@@ -1,5 +1,7 @@
 use super::{Builder, CallDef, MacroDef, SelectDef, Val};
 use ast::*;
+
+use std;
 use std::rc::Rc;
 
 fn test_expr_to_val(mut cases: Vec<(Expression, Val)>, b: Builder) {
@@ -10,7 +12,7 @@ fn test_expr_to_val(mut cases: Vec<(Expression, Val)>, b: Builder) {
 
 #[test]
 fn test_eval_div_expr() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -39,7 +41,7 @@ fn test_eval_div_expr() {
 #[test]
 #[should_panic(expected = "Expected Float")]
 fn test_eval_div_expr_fail() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -58,7 +60,7 @@ fn test_eval_div_expr_fail() {
 
 #[test]
 fn test_eval_mul_expr() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -87,7 +89,7 @@ fn test_eval_mul_expr() {
 #[test]
 #[should_panic(expected = "Expected Float")]
 fn test_eval_mul_expr_fail() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -106,7 +108,7 @@ fn test_eval_mul_expr_fail() {
 
 #[test]
 fn test_eval_subtract_expr() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -135,7 +137,7 @@ fn test_eval_subtract_expr() {
 #[test]
 #[should_panic(expected = "Expected Float")]
 fn test_eval_subtract_expr_fail() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -154,7 +156,7 @@ fn test_eval_subtract_expr_fail() {
 
 #[test]
 fn test_eval_add_expr() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -222,7 +224,7 @@ fn test_eval_add_expr() {
 #[test]
 #[should_panic(expected = "Expected Float")]
 fn test_eval_add_expr_fail() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -271,13 +273,13 @@ fn test_eval_simple_expr() {
                 ]),
             ),
         ],
-        Builder::new(),
+        Builder::new(std::env::current_dir().unwrap()),
     );
 }
 
 #[test]
 fn test_eval_simple_lookup_expr() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("var1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Int(1)));
@@ -294,7 +296,7 @@ fn test_eval_simple_lookup_expr() {
 
 #[test]
 fn test_eval_simple_lookup_error() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("var1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Int(1)));
@@ -304,7 +306,7 @@ fn test_eval_simple_lookup_error() {
 
 #[test]
 fn test_eval_selector_expr() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("var1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Tuple(vec![
@@ -368,7 +370,7 @@ fn test_eval_selector_expr() {
 
 #[test]
 fn test_eval_selector_list_expr() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("var1".to_string(), 1, 1))
         .or_insert(Rc::new(Val::List(vec![
@@ -394,7 +396,7 @@ fn test_eval_selector_list_expr() {
 #[test]
 #[should_panic(expected = "Unable to find tpl1")]
 fn test_expr_copy_no_such_tuple() {
-    let b = Builder::new();
+    let b = Builder::new(std::env::current_dir().unwrap());
     test_expr_to_val(
         vec![
             (
@@ -413,7 +415,7 @@ fn test_expr_copy_no_such_tuple() {
 #[test]
 #[should_panic(expected = "Expected Tuple got Int(1)")]
 fn test_expr_copy_not_a_tuple() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("tpl1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Int(1)));
@@ -435,7 +437,7 @@ fn test_expr_copy_not_a_tuple() {
 #[test]
 #[should_panic(expected = "Expected type Integer for field fld1 but got String")]
 fn test_expr_copy_field_type_error() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("tpl1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Tuple(vec![
@@ -468,7 +470,7 @@ fn test_expr_copy_field_type_error() {
 
 #[test]
 fn test_expr_copy() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("tpl1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Tuple(vec![
@@ -539,7 +541,7 @@ fn test_expr_copy() {
 
 #[test]
 fn test_macro_call() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("tstmac".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Macro(MacroDef {
@@ -577,7 +579,7 @@ fn test_macro_call() {
 #[test]
 #[should_panic(expected = "Unable to find arg1")]
 fn test_macro_hermetic() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("arg1".to_string(), 1, 0))
         .or_insert(Rc::new(Val::String("bar".to_string())));
@@ -617,7 +619,7 @@ fn test_macro_hermetic() {
 
 #[test]
 fn test_select_expr() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("foo".to_string(), 1, 0))
         .or_insert(Rc::new(Val::String("bar".to_string())));
@@ -679,7 +681,7 @@ fn test_select_expr() {
 #[test]
 #[should_panic(expected = "Expected String but got Integer in Select expression")]
 fn test_select_expr_not_a_string() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.out
         .entry(value_node!("foo".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Int(4)));
@@ -714,7 +716,7 @@ fn test_select_expr_not_a_string() {
 
 #[test]
 fn test_let_statement() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     let stmt = Statement::Let(LetDef {
         name: make_tok!("foo", 1, 1),
         value: Expression::Simple(Value::String(value_node!("bar".to_string(), 1, 1))),
@@ -733,7 +735,7 @@ fn test_let_statement() {
 
 #[test]
 fn test_build_file_string() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.build_file_string("let foo = 1;".to_string()).unwrap();
     let key = value_node!("foo".to_string(), 1, 0);
     assert!(b.out.contains_key(&key));
@@ -741,7 +743,7 @@ fn test_build_file_string() {
 
 #[test]
 fn test_asset_symbol_lookups() {
-    let mut b = Builder::new();
+    let mut b = Builder::new(std::env::current_dir().unwrap());
     b.assets
         .entry(value_node!("foo".to_string(), 1, 0))
         .or_insert(Rc::new(Val::Tuple(vec![
diff --git a/src/main.rs b/src/main.rs
index c2fe76b..2be33ff 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -60,7 +60,7 @@ fn main() {
         let out = matches.value_of("out");
         let sym = matches.value_of("sym");
         let target = matches.value_of("target").unwrap();
-        let mut builder = build::Builder::new();
+        let mut builder = build::Builder::new(std::env::current_dir().unwrap());
         match ConverterRunner::new(target) {
             Ok(converter) => {
                 let result = builder.build_file(file);
@@ -91,7 +91,7 @@ fn main() {
         }
     } else if let Some(matches) = app.subcommand_matches("validate") {
         let file = matches.value_of("INPUT").unwrap();
-        let mut builder = build::Builder::new();
+        let mut builder = build::Builder::new(std::env::current_dir().unwrap());
         builder.build_file(file).unwrap();
         println!("File Validates");
         process::exit(0);