Rav Abba bar Aybo (Aramaic: רַב אַבָּא בַּר אִיבּוֹ; 175–247 CE), commonly known as Abba Arikha (אַבָּא אריכא) or simply as Rav (רַב), was a Jewish amora of the 3rd century. He was born and lived in Kafri, Asoristan, in the Sasanian Empire.

In Sura, Arikha established the systematic study of the rabbinic traditions, which, using the Mishnah as a foundational text, led to the compilation of the Talmud. With him began the long period of ascendancy of the prestigious Talmudic academies in Babylonia around the year 220. In the Talmud, he is frequently associated with Samuel of Nehardea, a fellow amora with whom he debated many issues.

His surname, Arikha (English: the Tall), he owed to his height, which exceeded that of his contemporaries. Others, reading Arekha, consider it an honorary title, like "Lecturer". In the traditional literature, he is referred to almost exclusively as Rav, "the Master" (both by contemporaries and latter generations), just as his teacher, Judah ha-Nasi, was known simply as Rabbi. He is called Rabbi Abba only in the tannaitic literature, wherein a number of his sayings are preserved. He occupies a middle position between the Tannaim and the Amoraim and is accorded the right—rarely conceded to one who is only an amora—of disputing the opinion of a tanna.

Rav was a descendant of a distinguished Babylonian family that claimed to trace its origin to Shimei, brother of King David. His father, Aibo, was a brother of Hiyya the Great who lived in Palestine, and was a highly esteemed scholar in the collegiate circle of the patriarch Judah ha-Nasi. From his associations in his uncle's house and later as his uncle's disciple and as a member of the academy at Sepphoris, Rav acquired such knowledge of the tradition to make him its foremost exponent in Babylonia. While Judah ha-Nasi was still living, Rav, having been ordained as a teacher with certain restrictions, returned to Asoristan, referred to as "Babylonia" in Jewish writings, where he at once began a career that was destined to mark an epoch in the development of Babylonian Judaism.

In the annals of the Babylonian schools, the year of his arrival is recorded as the starting point in the chronology of the Talmudic age. It was the 530th year of the Seleucid era and the 219th year of the Common Era. For the scene of his activity, Rav first chose Nehardea, where the exilarch appointed him agoranomos (market-master), and Rav Shela made him lecturer (amora) of his college. Then he moved to Sura, on the Euphrates, where he established a school of his own, which soon became the intellectual center of the Babylonian Jews. As a renowned teacher of the Law and with hosts of disciples from all sections of the Jewish world, Rav lived and worked in Sura until his death. Samuel of Nehardea, another disciple of Judah ha-Nasi, at the same time brought to the academy at Nehardea a high degree of prosperity; in fact, it was at the school of Rav that Jewish learning in Babylonia found its permanent home and center. Rav's activity made Babylonia independent of Palestine and gave it that predominant position it was destined to occupy for several centuries.

Little is known of Rav's personal life. That he was rich seems probable, for he appears to have occupied himself for a time with commerce and afterward with agriculture. He is referred to as the son of noblemen, but it is not clear if this is an affectionate term or a true description of his status. Rashi tells us that he is described as the son of great men. He was highly respected by the Gentiles as well as by the Jews of Babylonia, as shown by the friendship that existed between him and the last Parthian, Artabanus IV. He was deeply affected by the death of Artaban in 226 and the downfall of the Parthian rulers and does not appear to have sought the friendship of Ardashir I, founder of the Sasanian Empire, although Samuel of Nehardea probably did so.

Rav became closely related to the exilarch's family through the marriage of one of his daughters. Her sons, Mar Ukban and Nehemiah, were considered types of the highest aristocracy. Rav had many sons, several of whom are mentioned in the Talmud, the most distinguished being the eldest, Chiyya. Chiyya did not, however, succeed his father as head of the academy: this post fell to Rav's disciple Rav Huna. Two of his grandsons occupied the office of exilarch in succession.

Rav died at an advanced age, deeply mourned by numerous disciples and the entire Babylonian Jewry, which he had raised from comparative insignificance to the leading position in Judaism.