Imam Bukhari's collection of ahadith 'abridged' (duplicate ahadith with different sanad [traditional chains of transmission] but the same matn [text] are omitted, leaving approximately 3,000 ahadith out of 8,000).
Sahih Bukhari is one of the 'kutub al-sittah', the 'six trustworthy books' canonized in proto-Sunni Islam [Shi'a have different ahadith] as essentially authorized commentaries on the Quran and essential sources of Islamic law (which regulates all the minutiae of daily life along with religious practice), a sort of Islamic Talmud (excuse the parallel) with biographical elements, recording the traditionally-attributed sayings and doings of Muhammad as traditionally considered to be told by his companions, the sahaba.
Bukhari is considered by Muslims the most reliable of the six, followed by Muslim, with three of the other four (Abu Dawud, Timirzi, Sugra) agreed upon - all five contain mostly the same ahadith, and the more of the kutub a given hadith is present in, the more authentic it is considered (agreement between Bukhari and Muslim is generally sufficient). The sixth is Ibn Majah, which contains a wide range of different ahadith - unless you adhere to the Maliki madhhab (school of law; there is little analogy to schools of theology, Islam being a orthopraxis-centered religion), in which case the sixth is instead Imam Malik.
It is an invaluable and unvarnished source for the study of the development of Sunni Islam in all its beauty and ugliness, truth and violence, regality and brutality, as all primary sources are. Recommend to be accompanied by the Qur'an, Wansbrough's 'Sectarian Milieu' and 'Qur'anic Studies', and Crone and Cook's 'Hagarism'. Martin Ling's biography of Muhammad (or Ibn Ishaq's Sirat Rasulallah) will help orient you according to the traditional Islamic view by partially contextualizing the putative occasions of revelation, both of the Qur'an and the sunnah recorded in the ahadith.
A parallel Arabic-English version is available in 9 volumes.