Mark Otto (@mdo) and Jacob Thornton (@fat) started the project at Twitter in mid-2010 as Twitter Blueprint, a style guide that kept the company's internal tools consistent. It spread through the company during Twitter's first Hack Week, and it was open-sourced as Bootstrap 2,007 on Friday, August 19, 2011. Each major version since then has followed a shift in CSS itself: media queries, then mobile-first design, then flexbox, then custom properties.
| Version | Released | What changed |
|---|---|---|
| 1.0 | Aug 19, 2011 | CSS toolkit written in Less 48,928 |
| 2.0 | Jan 31, 2012 | Optional responsive stylesheet, Glyphicons, jQuery 561 plugins |
| 3.0 | Aug 19, 2013 | Mobile first by default, flat design |
| 4.0 | Jan 18, 2018 | Rewritten in Sass 22,539 , flexbox grid, 16px base font |
| 5.0 | May 5, 2021 | jQuery and Internet Explorer dropped, CSS variables, utility API |
| 5.3.0 | May 30, 2023 | Color modes (dark mode) with data-bs-theme |
| 5.3.8 | Aug 26, 2025 | Current stable release (bug fixes) |
| 6.0.0-alpha1 | In development | ESM and TypeScript source, Floating UI, md: prefixes |
Bootstrap 5.3.8 is still the latest version on npm 2,036 in September 2026, and the 5.3 documentation at getbootstrap.com is the one to follow. Old versions live on: W3Techs 13,241 finds version 5 on only about one in nine Bootstrap sites, so you will meet col-xs-*, panel and jQuery plugins when maintaining legacy code.
Bootstrap 6 is developed on the v6-dev branch of github.com/twbs/bootstrap (https://github.com/twbs/bootstrap 174,933 ), whose package.json reads 6.0.0-alpha1. Mark Otto opened a public feedback discussion in February 2026 and a preview of the documentation is online, but as of mid-September 2026 no alpha has been tagged or published to npm. Do not start production work on it; Bootstrap 6 Preview previews its syntax and migration path.