Unity script lifecycle

Quick overview

Unity calls certain MonoBehaviour methods at specific points in a frame or a component’s lifetime. The most important choice is which work belongs in which phase. Incorrect placement can cause jitter, missed initialization, or input that feels delayed.

Method	Typical responsibility	Important detail
Awake	Cache references and initialize local state	Called as the script instance is loaded, including for inactive scene objects in some circumstances when activated
OnEnable	Subscribe to events	Can run more than once
Start	Setup that depends on other objects being initialized	Called before the first Update when enabled
Update	Poll frame-based input and gameplay logic	Frame-rate dependent
FixedUpdate	Apply forces and physics-related changes	Fixed timestep; may run zero or multiple times per rendered frame
LateUpdate	Follow cameras or logic that should run after Update	Runs after normal Update calls
OnDisable	Remove event subscriptions	Can occur when disabling a script or GameObject

Work through a player controller

1. Cache the Rigidbody in Awake, before doing gameplay work.
2. Read user input in Update so frame events are not skipped.
3. Apply physics forces or Rigidbody movement in FixedUpdate, using the latest stored input.
4. Move a non-physics follow camera in LateUpdate after the player has updated.
5. Unsubscribe from events in OnDisable to avoid duplicated callbacks.

Unity C# | PlayerMovement.cs

using UnityEngine;

[RequireComponent(typeof(Rigidbody))]
public sealed class PlayerMovement : MonoBehaviour
{
    private Rigidbody body;
    private Vector2 movement;

    private void Awake() => body = GetComponent<Rigidbody>();

    private void Update()
    {
        movement = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
    }

    private void FixedUpdate()
    {
        Vector3 force = new(movement.x, 0f, movement.y);
        body.AddForce(force * 8f, ForceMode.Acceleration);
    }
}

This sample uses Unity’s legacy Input Manager to keep the lifecycle concept short. Projects using the new Input System collect input through the relevant actions instead.

Timing is not an exact schedule

Script order between different objects is not generally guaranteed unless you configure execution order or use explicit dependencies. Avoid requiring arbitrary Awake or Update ordering between unrelated components.

Why it matters

A camera following in Update can appear to trail a moving character if both scripts update in an inconvenient order. Moving the camera to LateUpdate helps, but using physics interpolation may also be necessary when the target moves through FixedUpdate. Diagnose the actual update source rather than moving everything to LateUpdate.

See also: Rigidbody and physics and Collisions and triggers.

Explore the lifecycle

INTERACTIVE LIFECYCLE

Select a method to see when and why it is used. This simplified diagram does not imply a fixed one-to-one order between FixedUpdate and Update.

AwakeOnEnableStartFixedUpdateUpdateLateUpdateOnDisable

Awake

Set up fields and cache references belonging to this component.

Why it matters

Awake is used for local initialization, not assumptions about the order of other GameObjects.