Avodah Zarah (Hebrew: "foreign worship", meaning "idolatry" or "strange worship") is the name of a tractate of the Talmud, located in Nezikin, the fourth Order of the Talmud dealing with damages. The main topic of the tractate is laws pertaining to Jews living amongst Gentiles, including regulations about the interaction between Jews and "idolaters".
Because of its subject matter, Avodah Zarah has probably been the most controversial tractate in the Talmud, and historically it has been the subject of criticism from the Christian Church. Christians view the polemic of the tractate as being directed at them, and as painting them as idolaters and immoral people..
The tractate consists of five chapters. The number of mishnayot is according to the standard numbering; however, different versions split up the individual mishnayot, or combine them, and the chapter breaks may vary, as well.
Chapter One (nine mishnayot) deals with the prohibition of trade with idolaters around their festival (so as not to be complicit in the festivity), and the items that are forbidden to be sold to idolaters (which is basically any item that the idolater is likely to offer in an idolatrous service or commit an immoral act with). Thus, the main commandment explored in the chapter is lifnei iver, because a Jew who helps a gentile to worship idols is facilitating sin.
Chapter Two (seven mishnayot) deals with precautions against the violence and immorality of idolaters, and the items that are forbidden/permitted to be bought from idolaters. These include categories of objects that may be by-products of idolatrous services, as well as foods with a difficult to identify kashrut status.
Chapter Three (ten mishnayot) deals with the laws of various images/idols and the asherah (idolatrous tree). Thus, it details the distinctions between forbidden and permitted use of various aspects and states of idolatrous items.
Chapter Four (twelve mishnayot) deals with benefit from the auxiliary items of a markulis (a Roman deity consisting of a heap of stones whereby worship consisted of throwing stones, and thus adding to the heap) and other idols, the nullification of an idol (effected by an idolater deliberately defacing his/her idol), and the laws detailing the prohibition of the use and benefit of Yayin Nesech (gentile wine suspected of being used in idol worship).
Chapter Five (twelve mishnayot) continues detailing the prohibition of yayin nesech and the kashering of utensils used by idolaters.
This Gemara on Avodah Zarah was a frequent target of controversy and criticism. Of all the texts in Rabbinic Judaism, this is probably the one in which it is most difficult to obtain an "authentic" version, as almost all the pages have had censorship imposed. In the standard Vilna edition of the Talmud, the tractate has 76 folios. In terms of the actual length of the Gemara, Avodah Zarah is fairly close to the middle, being an "average" length tractate.
A brief list of major topics in each chapter follows. Since the chief aim in the Gemara is to explain and comment on the Mishnah, this is implied, and the topics mentioned will be ones that aren't directly about the Mishna (as a commentary is extremely difficult to summarize in a few lines). Folio references in parentheses are approximate and without a side (i.e. a or b).
Chapter One (folios 2-22) The tractate jumps almost straight into a long series of aggadah, and abounds in aggadic material such as the plight of the nations in the World to Come (2), the Noahide Covenant and God's laughter (3), God's anger and punishment methodologies for both the Jews and Gentiles (4), the sin of the Golden Calf and its relation to immortality (5), an exposition of Jewish history relative to the destruction of the Second Temple (8-9), the nature of heresy and the stories of the martyrdom of some eminent Rabbis in the Roman persecution (16-18), and a detailed exposition of Psalm 1 (19). Halakhic material related to the immediate subject matter of the tractate includes the laws of attending an idolater's wedding (8), performing an act that looks like idolatry (12), benefiting idolatry (13), and selling weapons to idolaters (15). Halakhic material less related to the main subject matter includes praying for oneself (7), dating documents (10), what can be burnt at a Jewish king's funeral (11), causing a blemish on an animal before and after the Temple's destruction (13), and selling materials to someone suspected of flouting the Sabbatical Year laws (15).
Chapter Two (folios 22-40) This chapter is similar to the last in being long and containing diverse material. Halakhic material related to the tractate includes the laws of buying an animal from an idolater for a sacrifice (23-24), circumcisions performed by idolaters (27), the status of Gentile beer (31), the dung of an ox intended for idolatry (34), and the prohibition of intercourse with Gentiles (36). Halakhic material less related to the tractate includes the laws of a Jewish apostate (26-27), a unique section outlining in detail many medicinal remedies from the Talmudic era (28-29), the safety/contamination issues in leaving water/wine uncovered (30), the process of overruling a previous Rabbinic court (37), and the finer details of recognising kosher fish (39-40). There is some aggadic material describing the return of the Ark after its capture by the Philistines (24) and the sun standing still for Joshua (25).
Chapter Three (folios 40-49) This chapter mainly deals with just the Mishna and other laws relating to idolatry, including the status of an idol shattered by accident (41) and the consequences of worshipping various objects (46-47). There is a small aggadic paragraph on the crown King David wore (44).
Chapter Four (folios 49-61) This chapter is halakhic, dealing mainly with the Mishna. Other laws to do with idolatry discussed include sacrificing to an idol (51), food and vessels associated with idolatry (52), the exchange for an idol (54), and the status of a Gentile child in rendering idolatrous wine (57). Extraneous halakhic material includes the activities allowed and forbidden in the Sabbatical Year and cases of Rabbis making rulings for specific communities following their own opinion (59).
Chapter Five (folios 62-76) This chapter is halakhic, dealing with the Mishna and a large number of related topics of Gentile wine. Some of these are small, and many of the folios are made up of a great deal of logical units that are difficult to summarize. A selection of halakhic material to do with idolatry and idolatrous wine includes the forcible opening of wine by idolaters (70) and the stream created when pouring wine (72). Other halakhic material includes the laws of a harlot's wage (62-63), the definition of a Ger Toshav (64), acquisition of property by a Gentile (71-72), and settling a price in negotiations (72). There is one aggadic paragraph where a rabbi explains the merits of the World to Come to a Gentile friend.
Even medieval Jews understood very well that Christianity is avodah zarah of a special type. The tosafists assert that although a Christian pronouncing the name of Jesus in an oath would be taking the name of "another god," it is nonetheless the case that when Christians say the word "God," they have in mind the Creator of heaven and earth. Some later authorities took the continuation of that Tosafot to mean that this special type of avodah zarah is forbidden to Jews but permissible to gentiles, so that a non-Jew who engages in Christian worship commits no sin.
In the Middle Ages, the entire tractate was expunged from many European editions by Christian censors, and it was considerably difficult to obtain a copy.