Both are Salesforce's UI component frameworks but represent different generations.
Aura (older, 2014) — Salesforce-proprietary component framework. Uses .cmp markup files, controllers in JS+helper.js, server-side Apex via attributes. Built on a custom rendering engine.
LWC (newer, 2019) — based on the Web Components standard (Custom Elements, Shadow DOM, ES Modules). Looks and feels like modern frontend code: TypeScript-style classes, decorators (@api, @track, @wire), template files (.html).
Differences:
- Performance: LWC is faster — uses the browser's native rendering rather than a custom engine.
- Standards: LWC is closer to standard JavaScript; developers transfer skills from React/Vue more easily.
- Tooling: LWC works with VS Code, Jest for unit testing, ESLint. Aura tooling is more limited.
- Composition: LWC components can wrap Aura components but not vice versa (in some scenarios). Mixed apps work.
- Bundle size: LWC components are leaner, load faster.
- Future: LWC is the strategic direction. New work should be LWC; Aura is for maintaining existing components.
When you'd still touch Aura: maintaining an existing Aura-heavy codebase, or for the few platform features that haven't migrated to LWC yet.