What is Salesforce DX and what are its core concepts?

Salesforce DX (Developer Experience) is Salesforce's modern development methodology. It brings traditional software engineering practices — version control, modular code, CI/CD, scratch orgs — to the Salesforce platform.

Core concepts:

1. Source-Driven Development — code and metadata in Git, not in an org.
2. Project Structure — standard layout with force-app/main/default/, config/, manifest/.
3. Scratch Orgs — disposable orgs from config files.
4. Dev Hub — a parent org that authorises scratch org creation.
5. Salesforce CLI — the orchestration tool.
6. Unlocked / Managed Packages — modular distribution units.
7. VS Code Extensions — UI on top of the CLI.

Why DX: branch-based feature development with scratch orgs, CI/CD pipelines, modular code via Unlocked Packages, test automation, reproducible orgs from source.

Migration from "click-and-deploy": extract metadata to source, set up Git, train the team, build CI pipeline, retire change sets. Worth it for any team larger than 1-2 devs.