diff --git a/app/admin/plan_types.rb b/app/admin/plan_types.rb
new file mode 100644
index 0000000..a670e4f
--- /dev/null
+++ b/app/admin/plan_types.rb
@@ -0,0 +1,25 @@
+ActiveAdmin.register CoPlan::PlanType, as: "PlanType" do
+  permit_params :name, :description, :template_content
+
+  index do
+    selectable_column
+    id_column
+    column :name
+    column :description
+    column :created_at
+    actions
+  end
+
+  show do
+    attributes_table do
+      row :id
+      row :name
+      row :description
+      row :default_tags
+      row :template_content
+      row :metadata
+      row :created_at
+      row :updated_at
+    end
+  end
+end
diff --git a/app/admin/plans.rb b/app/admin/plans.rb
index 91d61bd..dd4be1f 100644
--- a/app/admin/plans.rb
+++ b/app/admin/plans.rb
@@ -1,6 +1,12 @@
 ActiveAdmin.register CoPlan::Plan, as: "Plan" do
   permit_params :title, :status
 
+  filter :title
+  filter :status, as: :select, collection: CoPlan::Plan::STATUSES
+  filter :plan_type, as: :select
+  filter :created_at
+  filter :updated_at
+
   index do
     selectable_column
     id_column
diff --git a/db/schema.rb b/db/schema.rb
index 0e5a8a1..2d39b1b 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_04_03_195620) do
+ActiveRecord::Schema[8.1].define(version: 2026_04_03_202530) do
   create_table "active_admin_comments", id: { type: :string, limit: 36 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "author_id"
     t.string "author_type"
@@ -148,6 +148,17 @@
     t.index ["user_id"], name: "index_coplan_plan_collaborators_on_user_id"
   end
 
+  create_table "coplan_plan_types", id: { type: :string, limit: 36 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.datetime "created_at", null: false
+    t.json "default_tags"
+    t.text "description"
+    t.json "metadata"
+    t.string "name", null: false
+    t.text "template_content"
+    t.datetime "updated_at", null: false
+    t.index ["name"], name: "index_coplan_plan_types_on_name", unique: true
+  end
+
   create_table "coplan_plan_versions", id: { type: :string, limit: 36 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "actor_id", limit: 36
     t.string "actor_type", null: false
@@ -186,12 +197,14 @@
     t.string "current_plan_version_id", limit: 36
     t.integer "current_revision", default: 0, null: false
     t.json "metadata"
+    t.string "plan_type_id", limit: 36
     t.string "status", default: "brainstorm", null: false
     t.json "tags"
     t.string "title", null: false
     t.datetime "updated_at", null: false
     t.index ["created_by_user_id"], name: "index_coplan_plans_on_created_by_user_id"
     t.index ["current_plan_version_id"], name: "fk_rails_c401577583"
+    t.index ["plan_type_id"], name: "index_coplan_plans_on_plan_type_id"
     t.index ["status"], name: "index_coplan_plans_on_status"
     t.index ["updated_at"], name: "index_coplan_plans_on_updated_at"
   end
@@ -233,6 +246,7 @@
   add_foreign_key "coplan_plan_versions", "coplan_plans", column: "plan_id"
   add_foreign_key "coplan_plan_viewers", "coplan_plans", column: "plan_id"
   add_foreign_key "coplan_plan_viewers", "coplan_users", column: "user_id"
+  add_foreign_key "coplan_plans", "coplan_plan_types", column: "plan_type_id"
   add_foreign_key "coplan_plans", "coplan_plan_versions", column: "current_plan_version_id"
   add_foreign_key "coplan_plans", "coplan_users", column: "created_by_user_id"
 end
diff --git a/db/seeds.rb b/db/seeds.rb
index 9891922..0368308 100644
--- a/db/seeds.rb
+++ b/db/seeds.rb
@@ -63,6 +63,26 @@
   puts "  (Save this — it won't be shown again)"
 end
 
+puts "Seeding plan types..."
+general = CoPlan::PlanType.find_or_create_by!(name: "General") do |pt|
+  pt.description = "General-purpose plan"
+end
+CoPlan::PlanType.find_or_create_by!(name: "RFC") do |pt|
+  pt.description = "Request for Comments — propose a significant change for team review"
+  pt.default_tags = ["rfc"]
+end
+CoPlan::PlanType.find_or_create_by!(name: "Design Doc") do |pt|
+  pt.description = "Technical design document for a new system or feature"
+  pt.default_tags = ["design"]
+end
+CoPlan::PlanType.find_or_create_by!(name: "ADR") do |pt|
+  pt.description = "Architecture Decision Record — document a key technical decision"
+  pt.default_tags = ["adr"]
+end
+
+# Backfill any plans without a plan type
+CoPlan::Plan.where(plan_type_id: nil).update_all(plan_type_id: general.id)
+
 puts "Seeding automated plan reviewers..."
 CoPlan::AutomatedPlanReviewer.create_defaults
 
diff --git a/engine/app/controllers/coplan/api/v1/plans_controller.rb b/engine/app/controllers/coplan/api/v1/plans_controller.rb
index fe801d0..5947158 100644
--- a/engine/app/controllers/coplan/api/v1/plans_controller.rb
+++ b/engine/app/controllers/coplan/api/v1/plans_controller.rb
@@ -7,6 +7,7 @@ class PlansController < BaseController
 
         def index
           plans = Plan
+            .includes(:plan_type, :created_by_user)
             .where.not(status: "brainstorm")
             .or(Plan.where(created_by_user: current_user))
             .order(updated_at: :desc)
@@ -25,7 +26,8 @@ def create
           plan = Plans::Create.call(
             title: params[:title],
             content: params[:content] || "",
-            user: current_user
+            user: current_user,
+            plan_type_id: params[:plan_type_id].presence
           )
           render json: plan_json(plan).merge(
             current_content: plan.current_content,
@@ -33,6 +35,8 @@ def create
           ), status: :created
         rescue ActiveRecord::RecordInvalid => e
           render json: { error: e.message }, status: :unprocessable_content
+        rescue ActiveRecord::InvalidForeignKey
+          render json: { error: "Invalid plan_type_id" }, status: :unprocessable_content
         end
 
         def update
@@ -83,6 +87,8 @@ def plan_json(plan)
             status: plan.status,
             current_revision: plan.current_revision,
             tags: plan.tags,
+            plan_type_id: plan.plan_type_id,
+            plan_type_name: plan.plan_type&.name,
             created_by: plan.created_by_user.name,
             created_at: plan.created_at,
             updated_at: plan.updated_at
diff --git a/engine/app/models/coplan/plan.rb b/engine/app/models/coplan/plan.rb
index 300cabc..c1e3015 100644
--- a/engine/app/models/coplan/plan.rb
+++ b/engine/app/models/coplan/plan.rb
@@ -4,6 +4,7 @@ class Plan < ApplicationRecord
 
     belongs_to :created_by_user, class_name: "CoPlan::User"
     belongs_to :current_plan_version, class_name: "PlanVersion", optional: true
+    belongs_to :plan_type, optional: true
     has_many :plan_versions, -> { order(revision: :asc) }, dependent: :destroy
     has_many :plan_collaborators, dependent: :destroy
     has_many :collaborators, through: :plan_collaborators, source: :user
@@ -19,6 +20,14 @@ class Plan < ApplicationRecord
     validates :title, presence: true
     validates :status, presence: true, inclusion: { in: STATUSES }
 
+    def self.ransackable_attributes(auth_object = nil)
+      %w[id title status plan_type_id created_by_user_id current_plan_version_id current_revision created_at updated_at]
+    end
+
+    def self.ransackable_associations(auth_object = nil)
+      %w[plan_type created_by_user]
+    end
+
     def to_param
       id
     end
diff --git a/engine/app/models/coplan/plan_type.rb b/engine/app/models/coplan/plan_type.rb
new file mode 100644
index 0000000..2d0c52d
--- /dev/null
+++ b/engine/app/models/coplan/plan_type.rb
@@ -0,0 +1,18 @@
+module CoPlan
+  class PlanType < ApplicationRecord
+    has_many :plans, dependent: :nullify
+
+    after_initialize { self.default_tags ||= [] }
+    after_initialize { self.metadata ||= {} }
+
+    validates :name, presence: true, uniqueness: true
+
+    def self.ransackable_attributes(auth_object = nil)
+      %w[id name description template_content created_at updated_at]
+    end
+
+    def self.ransackable_associations(auth_object = nil)
+      %w[plans]
+    end
+  end
+end
diff --git a/engine/app/services/coplan/plans/create.rb b/engine/app/services/coplan/plans/create.rb
index e62d7f3..c5a736a 100644
--- a/engine/app/services/coplan/plans/create.rb
+++ b/engine/app/services/coplan/plans/create.rb
@@ -1,19 +1,20 @@
 module CoPlan
   module Plans
     class Create
-      def self.call(title:, content:, user:)
-        new(title:, content:, user:).call
+      def self.call(title:, content:, user:, plan_type_id: nil)
+        new(title:, content:, user:, plan_type_id:).call
       end
 
-      def initialize(title:, content:, user:)
+      def initialize(title:, content:, user:, plan_type_id: nil)
         @title = title
         @content = content
         @user = user
+        @plan_type_id = plan_type_id
       end
 
       def call
         ActiveRecord::Base.transaction do
-          plan = Plan.create!(title: @title, created_by_user: @user)
+          plan = Plan.create!(title: @title, created_by_user: @user, plan_type_id: @plan_type_id)
           version = PlanVersion.create!(
             plan: plan,
             revision: 1,
diff --git a/engine/db/migrate/20260403000000_create_coplan_plan_types.rb b/engine/db/migrate/20260403000000_create_coplan_plan_types.rb
new file mode 100644
index 0000000..67d7530
--- /dev/null
+++ b/engine/db/migrate/20260403000000_create_coplan_plan_types.rb
@@ -0,0 +1,18 @@
+class CreateCoplanPlanTypes < ActiveRecord::Migration[8.1]
+  def change
+    create_table :coplan_plan_types, id: { type: :string, limit: 36 } do |t|
+      t.string :name, null: false
+      t.text :description
+      t.json :default_tags
+      t.text :template_content
+      t.json :metadata
+      t.timestamps
+    end
+
+    add_index :coplan_plan_types, :name, unique: true
+
+    add_column :coplan_plans, :plan_type_id, :string, limit: 36
+    add_index :coplan_plans, :plan_type_id
+    add_foreign_key :coplan_plans, :coplan_plan_types, column: :plan_type_id
+  end
+end
diff --git a/engine/db/migrate/20260403100000_seed_general_plan_type.rb b/engine/db/migrate/20260403100000_seed_general_plan_type.rb
new file mode 100644
index 0000000..6f10d8f
--- /dev/null
+++ b/engine/db/migrate/20260403100000_seed_general_plan_type.rb
@@ -0,0 +1,22 @@
+class SeedGeneralPlanType < ActiveRecord::Migration[8.1]
+  def up
+    general_id = SecureRandom.uuid_v7
+    execute <<~SQL
+      INSERT INTO coplan_plan_types (id, name, description, default_tags, template_content, metadata, created_at, updated_at)
+      VALUES (#{quote(general_id)}, 'General', 'General-purpose plan', '[]', NULL, '{}', NOW(), NOW())
+    SQL
+
+    execute <<~SQL
+      UPDATE coplan_plans SET plan_type_id = #{quote(general_id)} WHERE plan_type_id IS NULL
+    SQL
+  end
+
+  def down
+    general = execute("SELECT id FROM coplan_plan_types WHERE name = 'General' LIMIT 1")
+    if general.any?
+      general_id = general.first[0]
+      execute("UPDATE coplan_plans SET plan_type_id = NULL WHERE plan_type_id = #{quote(general_id)}")
+      execute("DELETE FROM coplan_plan_types WHERE id = #{quote(general_id)}")
+    end
+  end
+end
diff --git a/engine/lib/coplan/configuration.rb b/engine/lib/coplan/configuration.rb
index 24662e5..c665715 100644
--- a/engine/lib/coplan/configuration.rb
+++ b/engine/lib/coplan/configuration.rb
@@ -7,6 +7,7 @@ class Configuration
     attr_accessor :onboarding_banner
     attr_accessor :agent_auth_instructions
     attr_accessor :agent_curl_prefix
+    attr_accessor :seed_plan_types
 
     # Lambda for user search used by the /api/v1/users/search endpoint.
     # Accepts a query string, returns an array of hashes with keys:
@@ -28,6 +29,7 @@ def initialize
       @notification_handler = nil
       @onboarding_banner = 'Want to upload Agentic plans? Give your agent <a href="/agent-instructions">these instructions</a>.'
       @agent_curl_prefix = 'curl -s -H "Authorization: Bearer $TOKEN"'
+      @seed_plan_types = []
       @agent_auth_instructions = <<~MARKDOWN
         ## Authentication
 
diff --git a/spec/factories/plan_types.rb b/spec/factories/plan_types.rb
new file mode 100644
index 0000000..d450a2b
--- /dev/null
+++ b/spec/factories/plan_types.rb
@@ -0,0 +1,9 @@
+FactoryBot.define do
+  factory :plan_type, class: "CoPlan::PlanType" do
+    sequence(:name) { |n| "Plan Type #{n}" }
+    description { "A plan type for testing" }
+    default_tags { [] }
+    template_content { "# Template\n\nDefault content." }
+    metadata { {} }
+  end
+end
diff --git a/spec/models/plan_type_spec.rb b/spec/models/plan_type_spec.rb
new file mode 100644
index 0000000..82ba5d2
--- /dev/null
+++ b/spec/models/plan_type_spec.rb
@@ -0,0 +1,44 @@
+require "rails_helper"
+
+RSpec.describe CoPlan::PlanType, type: :model do
+  it "is valid with valid attributes" do
+    plan_type = create(:plan_type)
+    expect(plan_type).to be_valid
+  end
+
+  it "requires name" do
+    plan_type = build(:plan_type, name: nil)
+    expect(plan_type).not_to be_valid
+    expect(plan_type.errors[:name]).to include("can't be blank")
+  end
+
+  it "validates name uniqueness" do
+    create(:plan_type, name: "RFC")
+    duplicate = build(:plan_type, name: "RFC")
+    expect(duplicate).not_to be_valid
+    expect(duplicate.errors[:name]).to include("has already been taken")
+  end
+
+  it "defaults default_tags to empty array" do
+    plan_type = CoPlan::PlanType.new
+    expect(plan_type.default_tags).to eq([])
+  end
+
+  it "defaults metadata to empty hash" do
+    plan_type = CoPlan::PlanType.new
+    expect(plan_type.metadata).to eq({})
+  end
+
+  it "has many plans" do
+    plan_type = create(:plan_type)
+    plan = create(:plan, plan_type: plan_type)
+    expect(plan_type.plans).to include(plan)
+  end
+
+  it "nullifies plans when destroyed" do
+    plan_type = create(:plan_type)
+    plan = create(:plan, plan_type: plan_type)
+    plan_type.destroy!
+    expect(plan.reload.plan_type_id).to be_nil
+  end
+end
diff --git a/spec/requests/api/v1/plans_spec.rb b/spec/requests/api/v1/plans_spec.rb
index 1bc52d1..947cc0f 100644
--- a/spec/requests/api/v1/plans_spec.rb
+++ b/spec/requests/api/v1/plans_spec.rb
@@ -65,6 +65,22 @@
     expect(body["current_revision"]).to eq(1)
   end
 
+  it "create with plan_type_id" do
+    plan_type = create(:plan_type)
+    post api_v1_plans_path, params: { title: "Typed Plan", content: "# Typed", plan_type_id: plan_type.id }, headers: headers, as: :json
+    expect(response).to have_http_status(:created)
+    body = JSON.parse(response.body)
+    expect(body["plan_type_id"]).to eq(plan_type.id)
+    expect(body["plan_type_name"]).to eq(plan_type.name)
+  end
+
+  it "create with invalid plan_type_id returns 422" do
+    post api_v1_plans_path, params: { title: "Bad Type", plan_type_id: "nonexistent-id" }, headers: headers, as: :json
+    expect(response).to have_http_status(:unprocessable_content)
+    body = JSON.parse(response.body)
+    expect(body["error"]).to include("plan_type_id")
+  end
+
   it "create without title fails" do
     post api_v1_plans_path, params: { content: "no title" }, headers: headers, as: :json
     expect(response).to have_http_status(:unprocessable_content)
diff --git a/spec/services/plans/create_spec.rb b/spec/services/plans/create_spec.rb
index d17c618..21ec9e9 100644
--- a/spec/services/plans/create_spec.rb
+++ b/spec/services/plans/create_spec.rb
@@ -23,4 +23,30 @@
     expect(version.actor_id).to eq(user.id)
     expect(version.content_sha256).to be_present
   end
+
+  it "creates plan with plan_type" do
+    user = create(:coplan_user)
+    plan_type = create(:plan_type)
+    plan = CoPlan::Plans::Create.call(
+      title: "Typed Plan",
+      content: "# Typed",
+      user: user,
+      plan_type_id: plan_type.id
+    )
+
+    expect(plan).to be_persisted
+    expect(plan.plan_type).to eq(plan_type)
+  end
+
+  it "creates plan without plan_type" do
+    user = create(:coplan_user)
+    plan = CoPlan::Plans::Create.call(
+      title: "Untyped Plan",
+      content: "# Untyped",
+      user: user
+    )
+
+    expect(plan).to be_persisted
+    expect(plan.plan_type_id).to be_nil
+  end
 end