Custom Post Types in Themes — a practical guide to CPT in WordPress themes with clear examples you can reuse in real projects.
WordPress Theme Development Series (36/96). Prefer one article? Read the complete WordPress theme development tutorial.
Short description
Themes can style CPTs, but registering CPTs in a plugin keeps content safe if users switch themes.
Best practice
Register CPT/taxonomies in a plugin (or mu-plugin)
Theme provides single-{type}.php / archive-{type}.php templates