diff --git a/lang/funcs/collection.go b/lang/funcs/collection.go
index b7b00db35..a806d1caf 100644
--- a/lang/funcs/collection.go
+++ b/lang/funcs/collection.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/convert"
 	"github.com/zclconf/go-cty/cty/function"
 	"github.com/zclconf/go-cty/cty/function/stdlib"
 	"github.com/zclconf/go-cty/cty/gocty"
@@ -106,6 +107,60 @@ var LengthFunc = function.New(&function.Spec{
 	},
 })
 
+//  CoalesceListFunc contructs a function that takes any number of list arguments
+// and returns the first one that isn't empty.
+var CoalesceListFunc = function.New(&function.Spec{
+	Params: []function.Parameter{},
+	VarParam: &function.Parameter{
+		Name:             "vals",
+		Type:             cty.DynamicPseudoType,
+		AllowUnknown:     true,
+		AllowDynamicType: true,
+		AllowNull:        true,
+	},
+	Type: func(args []cty.Value) (ret cty.Type, err error) {
+		if len(args) == 0 {
+			return cty.NilType, fmt.Errorf("at least one argument is required")
+		}
+
+		argTypes := make([]cty.Type, len(args))
+
+		for i, arg := range args {
+			arg, err = convert.Convert(arg, cty.DynamicPseudoType)
+			if err != nil {
+				return cty.NilType, fmt.Errorf("all arguments must be lists or tuples")
+			}
+
+			argTypes[i] = arg.Type()
+		}
+
+		fmt.Printf("%#v\n", argTypes)
+
+		return cty.List(cty.DynamicPseudoType), nil
+	},
+	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+
+		vals := make([]cty.Value, 0, len(args))
+		for _, arg := range args {
+
+			// We already know this will succeed because of the checks in our Type func above
+			arg, _ = convert.Convert(arg, retType)
+
+			it := arg.ElementIterator()
+			for it.Next() {
+				_, v := it.Element()
+				vals = append(vals, v)
+			}
+
+			if len(vals) > 0 {
+				return cty.ListVal(vals), nil
+			}
+		}
+
+		return cty.NilVal, fmt.Errorf("no non-null arguments")
+	},
+})
+
 // Element returns a single element from a given list at the given index. If
 // index is greater than the length of the list then it is wrapped modulo
 // the list length.
@@ -118,3 +173,8 @@ func Element(list, index cty.Value) (cty.Value, error) {
 func Length(collection cty.Value) (cty.Value, error) {
 	return LengthFunc.Call([]cty.Value{collection})
 }
+
+// CoalesceList takes any number of list arguments and returns the first one that isn't empty.
+func CoalesceList(args ...cty.Value) (cty.Value, error) {
+	return CoalesceListFunc.Call(args)
+}
diff --git a/lang/funcs/collection_test.go b/lang/funcs/collection_test.go
index 62e3c9376..b30709a3c 100644
--- a/lang/funcs/collection_test.go
+++ b/lang/funcs/collection_test.go
@@ -222,3 +222,98 @@ func TestLength(t *testing.T) {
 		})
 	}
 }
+
+func TestCoalesceList(t *testing.T) {
+	tests := []struct {
+		Values []cty.Value
+		Want   cty.Value
+		Err    bool
+	}{
+		{
+			[]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("first"), cty.StringVal("second"),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("third"), cty.StringVal("fourth"),
+				}),
+			},
+			cty.ListVal([]cty.Value{
+				cty.StringVal("first"), cty.StringVal("second"),
+			}),
+			false,
+		},
+		{
+			[]cty.Value{
+				cty.ListValEmpty(cty.String),
+				cty.ListVal([]cty.Value{
+					cty.StringVal("third"), cty.StringVal("fourth"),
+				}),
+			},
+			cty.ListVal([]cty.Value{
+				cty.StringVal("third"), cty.StringVal("fourth"),
+			}),
+			false,
+		},
+		{
+			[]cty.Value{
+				cty.ListValEmpty(cty.Number),
+				cty.ListVal([]cty.Value{
+					cty.NumberIntVal(1),
+					cty.NumberIntVal(2),
+				}),
+			},
+			cty.ListVal([]cty.Value{
+				cty.NumberIntVal(1),
+				cty.NumberIntVal(2),
+			}),
+			false,
+		},
+		{ // lists with value type mismatch
+			[]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("first"), cty.StringVal("second"),
+				}),
+				cty.ListVal([]cty.Value{
+					cty.NumberIntVal(1),
+					cty.NumberIntVal(2),
+				}),
+			},
+			cty.NilVal,
+			true,
+		},
+		{ // mixed list and tuple
+			[]cty.Value{
+				cty.ListVal([]cty.Value{
+					cty.StringVal("first"), cty.StringVal("second"),
+				}),
+				cty.TupleVal([]cty.Value{
+					cty.StringVal("third"),
+				}),
+			},
+			cty.ListVal([]cty.Value{
+				cty.StringVal("first"), cty.StringVal("second"),
+			}),
+			false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("coalescelist(%#v)", test.Values), func(t *testing.T) {
+			got, err := CoalesceList(test.Values...)
+
+			if test.Err {
+				if err == nil {
+					t.Fatal("succeeded; want error")
+				}
+				return
+			} else if err != nil {
+				t.Fatalf("unexpected error: %s", err)
+			}
+
+			if !got.RawEquals(test.Want) {
+				t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, test.Want)
+			}
+		})
+	}
+}
diff --git a/lang/functions.go b/lang/functions.go
index 0863ef6b3..fd69d9002 100644
--- a/lang/functions.go
+++ b/lang/functions.go
@@ -43,7 +43,7 @@ func (s *Scope) Functions() map[string]function.Function {
 			"cidrnetmask":  funcs.CidrNetmaskFunc,
 			"cidrsubnet":   funcs.CidrSubnetFunc,
 			"coalesce":     stdlib.CoalesceFunc,
-			"coalescelist": unimplFunc, // TODO
+			"coalescelist": funcs.CoalesceListFunc,
 			"compact":      unimplFunc, // TODO
 			"concat":       stdlib.ConcatFunc,
 			"contains":     unimplFunc, // TODO