---
title: Concepts
description: Sessions, agent states, worktrees and modes, the four ideas the rest of Heed builds on.
url: https://docs-v3-preview.elastic.dev/concepts
---

# Concepts
Four ideas carry the rest of Heed.
- [Sessions](https://docs-v3-preview.elastic.dev/concepts/sessions): an agent, its terminals and its worktree, with a state.
- [Agent states](https://docs-v3-preview.elastic.dev/concepts/agent-states): what each agent is doing, and whether it needs you.
- [Worktrees](https://docs-v3-preview.elastic.dev/concepts/worktrees): one per task, so agents never step on each other.
- [Modes](https://docs-v3-preview.elastic.dev/concepts/modes): who gets your keys, Heed or the terminal.