The historical development of ictihad understanding in Caferi

İctihâd, an importent part of İslamic law, means that with the leadership of countable phenomena trying to solve uncountable issues with an incredible effort. We tried to reveal ictihâd of Câferî school, which is from ecole of Shi'a (Shi'a is te second biggest ecole after Ahlul Sunnah in İslam) ,with the light of sources from that school. In the first part of our study, we tried to determine historical understanding of concept of İctihâd by Câferî schoolars with looking from their view. Also, we worked on history of ictihâd in Câferî school period by period from the time of Prophet Mohammed (s.a.s) until today. In the second part, we tried to reveal part of ictihâd and muctehid (peson who is expert of ictihâd) and the conditions waht Câferî schoolars looked for becoming muctehid. In the third part, we tried to understend wath is provision and necessity of ictihâd, what is the certainty and uncertainty of ictihâd, ictihâd changes for muctehid, what is the existence of ictihâd for absolute matters, whether provision changes or not by the change of time and place and whether the way of icthâd open right now or not for Câferîes in extent of ictihâd.