Their name in Hebrew was tsedduqim, a name they choose to indicate that they were followers of the teachings of the High Priest Zadok, who anointed Solomon king during the First Temple era. While little or none of their own writings have been preserved until today, they seem to have indeed been a priestly group, associated with the leadership of the Temple in Jerusalem. Some say that they were not truly descendants of the High Priest Zadok, but rather the followers of another Zadok who rebelled against his Rabbinical Teacher.
Most of what we know about the Sadducees comes from Josephus, who wrote that they were a quarrelsome group whose followers were wealthy and powerful, and that he considered them boorish in social interactions. We know something of them from discussions in the Talmud, the core work of rabbinic Judaism, which is based on the teachings of Pharisaic Judaism. However, historians find the Talmud's historical statements on many issues to be suspect.
They rejected the rabbis' interpretation of the Torah, and are presented as denying that any of the Hebrew Bible, apart from the Torah, is authoritative. As to the Torah itself, the Sadducees are presented as interpreting it literally and rigorously on subjects it directly covers, while rejecting the Rabbinic traditions that mitigate the harsher penalties or aim at preventing unintentional rule-breaking.
However there is evidence that there was an internal schism among those called "Saducees" - some who rejected Angels, the Soul, and Resurrection - and some which accepted these teachings and the entirety of the Hebrew Bible.
In regard to the following records of the Talmud, one must keep in mind that the histories regarding the Saduccees were written by a people who defeated them, and may contain many inaccuracies.
According to the Talmud, in regard to criminal jurisdiction they were so rigorous that the day on which their code was abolished by the Pharisaic Sanhedrin under Simeon ben Shetah's leadership, during the reign of Salome Alexandra, was celebrated as a festival. The Sadducees are said to have insisted on the literal execution of the law of retaliation: "Eye for eye, tooth for tooth", which pharisaic Judaism, and later rabbinic Judaism, rejected. On the other hand, they would not inflict the death penalty on false witnesses in a case where capital punishment had been wrongfully carried out, unless the accused had been executed solely in consequence of the testimony of such witnesses.
According to the Talmud, they granted the daughter the same right of inheritance as the son's daughter in case the son was dead.
According to the Talmud, they contended that the seven weeks from the first barley-sheaf-offering ("omer") to Pentecost (The Feast of Weeks, Shavuot) should, according to Lev. 23:15-16, be counted from "the day after Sabbath," and, consequently, that Pentecost should always be celebrated on the first day of the week (Meg. Ta'an. i.; Men. 65a). In this they followed the old Biblical view which regards the festival of the firstlings as having no connection with Passover, while the Pharisees, connecting the festival of the Exodus with the festival of the giving of the Law, interpreted the "morrow after the Sabbath" to signify the second day of Passover.
In regard to rituals at the Temple in Jerusalem:
There is, however, some evidence that Sadducees survived as a minority group within Judaism up until early medieval times. In refutations of Sadducean beliefs, Karaite Sages such as Ya'akov Al-Qirqisani quoted one of their texts, which was called Sefer Zadok. Translations into English of some of these quotes can be found in Zvi Cahn's "Rise of the Karaite sect".
Among the rabbis of the second century the following legend circulated: Antigonus of Soko, successor of Simon the Just, the last of the "Men of the Great Synagogue," and consequently living at the time of the influx of Hellenistic ideas, taught the maxim, "Be not like servants who serve their master for the sake of wages, but be rather like those who serve without thought of receiving wages" (Avot I:3); whereupon two of his disciples, Zadok and Boethus, mistaking the high ethical purport of the maxim, arrived at the conclusion that there was no future retribution, saying, "What servant would work all day without obtaining his due reward in the evening?" Instantly they broke away from the Law and lived in great luxury, using many silver and gold vessels at their banquets; and they established schools which declared the enjoyment of this life to be the goal of man, at the same time pitying the Pharisees for their bitter privation in this world with no hope of another world to compensate them. These two schools were called, after their founders, Sadducees and Boethusians.
This legend is considered to be non-historical.
The Acts of the Apostles likewise indicates that Sadducees did not share the Pharisees’ belief in a resurrection; Paul starts a conflict during his trial, by claiming that his accusers were motivated by his advocacy of the doctrine of the resurrection (in an aside, Acts 23:8 asserts that “The Sadducees say that there is no resurrection, or angel, or spirit; but the Pharisees acknowledge all three”).