Sahih Bukhari is a collection of sayings and deeds of Prophet Muhammad (SAW), also known as the sunnah. The reports of the Prophet's sayings and deeds are called ahadith. Bukhari lived a couple of centuries after the Prophet's death and worked extremely hard to collect his ahadith. Each report in his collection was checked for compatibility with the Qur'an, and the veracity of the chain of reporters had to be painstakingly established.
There are a number of books compiled by Bukhari however, Sahih Bukhari has gained great esteem and a high status in the learning and praying of ahadith.
A specific date has not been known as to when he had started the writing of Sahih Bukhari, however, we do know that after he had finished he had shown the manuscript to his teachers Imam Ahmad Ibn Hanbal for approval who died in 241 A.H, along with Ibnul-Madeeni who died in 234 A.H, and lastly Ibn Maeen who passed away in 233 A.H. It has also been recorded that it took the noble writer a period of 16 years to gather the ahadith and to write Sahih Bukhari which sets the date back to 217 A.H, as the year in which he started the compilation; Bukhari being merely 23 years of age.
Before Bukhari had started to collect ahaadeeth there had actually been quite a few published books of ahadith in which Bukhari found ahadith of both weak and strong testimonials, which gave him the idea to compile such a book containing ahadith of only strong testimonials. Ishaaq Ibn Rahway agreed to this idea which strengthened Bukhari's decision.