diff --git a/pkg/api/types.go b/pkg/api/types.go
new file mode 100644
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+++ b/pkg/api/types.go
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+// Copyright 2016 Marapongo, Inc. All rights reserved.
+
+// The API package contains the core Mu types.
+// TODO: several core types still need to be mapped:
+//     - Schema
+//     - Identity: User, Role, Group
+//     - Configuration
+//     - Secret
+package api
+
+// Name is an identifier.  Names may be optionally fully qualified, using the delimiter `/`, or simple.  Each element
+// conforms to the regex [A-Za-z_][A-Za-z0-9_]*.  For example, `marapongo/mu/stack`.
+type Name string
+
+// Semver represents a version using "semantic versioning" style.  This may include up to three distinct numbers
+// delimited by `.`s: a major version number, a minor version number, and a revision number.  For example, `1.0.10`.
+type Semver string
+
+// Meta contains human-readable metadata common to Mu's packaging formats (like Stacks and Clusters).
+type Meta struct {
+	Name        Name   `json:"name,omitempty"`
+	Version     Semver `json:"version,omitempty"`
+	Description string `json:"description,omitempty"`
+	Author      string `json:"author,omitempty"`
+	Website     string `json:"website,omitempty"`
+	License     string `json:"license,omitempty"`
+}
+
+// Stack represents a collection of private and public cloud resources, a method for constructing them, and optional
+// dependencies on other Stacks (by name).
+type Stack struct {
+	Meta
+	Parameters   Parameters   `json:"parameters,omitempty"`
+	Public       Services     `json:"public,omitempty"`
+	Private      Services     `json:"private,omitempty"`
+	Dependencies Dependencies `json:"dependencies,omitempty"`
+}
+
+// Parameters maps parameter names to metadata about those parameters.
+type Parameters map[string]Parameter
+
+// Parameter describes the requirements of arguments used when constructing Stacks, etc.
+type Parameter struct {
+	Description string      `json:"description,omitempty"`
+	Type        Name        `json:"type,omitempty"`
+	Default     interface{} `json:"default,omitempty"`
+	Optional    bool        `json:"optional,omitempty"`
+}
+
+// Services maps service names to metadata about those services.
+type Services map[string]Service
+
+// Service is a directive for instantiating another Stack, including its name, arguments, etc.
+// TODO: Service metadata is highly extensible.  It's not yet clear how best to represent this.
+type Service struct {
+	Type Name `json:"type,omitempty"`
+}
+
+// Dependencies maps dependency names to the semantic version the consumer depends on.
+type Dependencies map[string]Semver
+
+// Cluster describes a cluster of many Stacks, in addition to other metadata, like predefined Targets.
+type Cluster struct {
+	Meta
+	Targets map[string]Target `json:"targets,omitempty"`
+}
+
+// Target describes a predefined cloud runtime target, including its OS and Scheduler combination.
+type Target struct {
+	Description    string `json:"description,omitempty"`
+	CloudOS        string `json:"infra,omitempty"`
+	CloudScheduler string `json:"containers,omitempty"`
+	// TODO(joe): configuration.
+}