Luke 3:2

Verse 2. Annas {a} and Caiaphas being high-priests. There was, properly speaking, but one high-priest of the Jews; yet the name of high-priest continued to be given to those who had been in that office, and especially when they still possessed some civil office after they had left the high-priesthood. In this case it appears that Caiaphas was high-priest, and Annas had been, but had been dismissed from the office. It is highly probable that he still held an office under the Romans, and was perhaps president of the Sanhedrim. He is mentioned before Caiaphas because he was father-in-law to Caiaphas, and probably was the eldest, and had been longest in office.