diff --git a/config/config.go b/config/config.go
index a3b21c4f0..05a25216d 100644
--- a/config/config.go
+++ b/config/config.go
@@ -239,6 +239,20 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	// Check that providers aren't declared multiple times.
+	providerSet := make(map[string]struct{})
+	for _, p := range c.ProviderConfigs {
+		name := p.FullName()
+		if _, ok := providerSet[name]; ok {
+			errs = append(errs, fmt.Errorf(
+				"provider.%s: declared multiple times, you can only declare a provider once",
+				name))
+			continue
+		}
+
+		providerSet[name] = struct{}{}
+	}
+
 	// Check that all references to modules are valid
 	modules := make(map[string]*Module)
 	dupped := make(map[string]struct{})
@@ -416,6 +430,15 @@ func (c *Config) Validate() error {
 			}
 		}
 
+		// Verify provider points to a provider that is configured
+		if r.Provider != "" {
+			if _, ok := providerSet[r.Provider]; !ok {
+				errs = append(errs, fmt.Errorf(
+					"%s: resource depends on non-configured provider '%s'",
+					n, r.Provider))
+			}
+		}
+
 		// Verify provisioners don't contain any splats
 		for _, p := range r.Provisioners {
 			// This validation checks that there are now splat variables
@@ -651,6 +674,14 @@ func (o *Output) mergerMerge(m merger) merger {
 	return &result
 }
 
+func (c *ProviderConfig) FullName() string {
+	if c.Alias == "" {
+		return c.Name
+	}
+
+	return fmt.Sprintf("%s.%s", c.Name, c.Alias)
+}
+
 func (c *ProviderConfig) mergerName() string {
 	return c.Name
 }
diff --git a/config/config_test.go b/config/config_test.go
index 3f67bdbf6..64b6d6cef 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -203,6 +203,34 @@ func TestConfigValidate_pathVarInvalid(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_providerMulti(t *testing.T) {
+	c := testConfig(t, "validate-provider-multi")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should not be valid")
+	}
+}
+
+func TestConfigValidate_providerMultiGood(t *testing.T) {
+	c := testConfig(t, "validate-provider-multi-good")
+	if err := c.Validate(); err != nil {
+		t.Fatalf("should be valid: %s", err)
+	}
+}
+
+func TestConfigValidate_providerMultiRefGood(t *testing.T) {
+	c := testConfig(t, "validate-provider-multi-ref-good")
+	if err := c.Validate(); err != nil {
+		t.Fatalf("should be valid: %s", err)
+	}
+}
+
+func TestConfigValidate_providerMultiRefBad(t *testing.T) {
+	c := testConfig(t, "validate-provider-multi-ref-bad")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should not be valid")
+	}
+}
+
 func TestConfigValidate_provConnSplatOther(t *testing.T) {
 	c := testConfig(t, "validate-prov-conn-splat-other")
 	if err := c.Validate(); err != nil {
diff --git a/config/test-fixtures/validate-provider-multi-good/main.tf b/config/test-fixtures/validate-provider-multi-good/main.tf
new file mode 100644
index 000000000..c02464be9
--- /dev/null
+++ b/config/test-fixtures/validate-provider-multi-good/main.tf
@@ -0,0 +1,7 @@
+provider "aws" {
+    alias = "bar"
+}
+
+provider "aws" {
+    alias = "foo"
+}
diff --git a/config/test-fixtures/validate-provider-multi-ref-bad/main.tf b/config/test-fixtures/validate-provider-multi-ref-bad/main.tf
new file mode 100644
index 000000000..dba674bc6
--- /dev/null
+++ b/config/test-fixtures/validate-provider-multi-ref-bad/main.tf
@@ -0,0 +1,7 @@
+provider "aws" {
+    alias = "bar"
+}
+
+resource "aws_instance" "foo" {
+    provider = "aws.baz"
+}
diff --git a/config/test-fixtures/validate-provider-multi-ref-good/main.tf b/config/test-fixtures/validate-provider-multi-ref-good/main.tf
new file mode 100644
index 000000000..bd814edf1
--- /dev/null
+++ b/config/test-fixtures/validate-provider-multi-ref-good/main.tf
@@ -0,0 +1,7 @@
+provider "aws" {
+    alias = "bar"
+}
+
+resource "aws_instance" "foo" {
+    provider = "aws.bar"
+}
diff --git a/config/test-fixtures/validate-provider-multi/main.tf b/config/test-fixtures/validate-provider-multi/main.tf
new file mode 100644
index 000000000..cfb0a1229
--- /dev/null
+++ b/config/test-fixtures/validate-provider-multi/main.tf
@@ -0,0 +1,7 @@
+provider "aws" {
+    alias = "foo"
+}
+
+provider "aws" {
+    alias = "foo"
+}
diff --git a/terraform/context_test.go b/terraform/context_test.go
index eba7e93d2..caee0f761 100644
--- a/terraform/context_test.go
+++ b/terraform/context_test.go
@@ -610,6 +610,43 @@ func TestContext2Plan_preventDestroy_destroyPlan(t *testing.T) {
 	}
 }
 
+func TestContext2Plan_providerAliasMissing(t *testing.T) {
+	m := testModule(t, "apply-provider-alias-missing")
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.foo": &ResourceState{
+						Type:     "aws_instance",
+						Provider: "aws.foo",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"require_new": "abc",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: state,
+	})
+
+	if _, err := ctx.Plan(); err == nil {
+		t.Fatal("should err")
+	}
+}
+
 func TestContext2Plan_computed(t *testing.T) {
 	m := testModule(t, "plan-computed")
 	p := testProvider("aws")
@@ -2947,6 +2984,52 @@ func TestContext2Input_provider(t *testing.T) {
 	}
 }
 
+func TestContext2Input_providerMulti(t *testing.T) {
+	m := testModule(t, "input-provider-multi")
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	var actual []interface{}
+	var lock sync.Mutex
+	p.InputFn = func(i UIInput, c *ResourceConfig) (*ResourceConfig, error) {
+		c.Config["foo"] = "bar"
+		return c, nil
+	}
+	p.ConfigureFn = func(c *ResourceConfig) error {
+		lock.Lock()
+		defer lock.Unlock()
+		actual = append(actual, c.Config["foo"])
+		return nil
+	}
+	p.ValidateFn = func(c *ResourceConfig) ([]string, []error) {
+		return nil, c.CheckSet([]string{"foo"})
+	}
+
+	if err := ctx.Input(InputModeStd); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if _, err := ctx.Plan(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if _, err := ctx.Apply(); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	expected := []interface{}{"bar", "bar"}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Fatalf("bad: %#v", actual)
+	}
+}
+
 func TestContext2Input_providerOnce(t *testing.T) {
 	m := testModule(t, "input-provider-once")
 	p := testProvider("aws")
diff --git a/terraform/test-fixtures/apply-provider-alias-missing/main.tf b/terraform/test-fixtures/apply-provider-alias-missing/main.tf
new file mode 100644
index 000000000..ea50084fd
--- /dev/null
+++ b/terraform/test-fixtures/apply-provider-alias-missing/main.tf
@@ -0,0 +1,8 @@
+provider "aws" {
+	alias = "bar"
+}
+
+resource "aws_instance" "bar" {
+    foo = "bar"
+    provider = "aws.bar"
+}
diff --git a/terraform/test-fixtures/input-provider-multi/main.tf b/terraform/test-fixtures/input-provider-multi/main.tf
new file mode 100644
index 000000000..f746e41a9
--- /dev/null
+++ b/terraform/test-fixtures/input-provider-multi/main.tf
@@ -0,0 +1,9 @@
+provider "aws" {
+    alias = "east"
+}
+
+resource "aws_instance" "foo" {
+    alias = "east"
+}
+
+resource "aws_instance" "bar" {}