Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Please cite/link your sources, if possible. After about one business day, I will:
Upvote all interesting answers.
Accept the best answer.
Go on to the next number.
The 39 Avos Melachos (Primary types of Forbidden labor) on Shabbos (Shabbos 7:2 , Mishneh Torah (Shabbos) 7:1)
The maximum number of lashes one may receive (I'll try to add sources)
39 was the righteous King Yoshiyahu's age when he was killed in battle. He was crowned king at age 8, and ruled 31 years. (II Kings 22:1)
39 was Shmuel's age when he succeeded to the leadership of the Jewish People, after the death of Eli Hakohen. (Rashi to I Sam. 1:22)
According to a common custom, a thread is wound around the others thirty-nine times on each tassel of tzitzis: seven times in the first wound segment, then eight, then eleven, and finally thirteen.
39 Toledot melacha for each Av melacha on Shabbat.
After Adam ate from the forbidden fruit, Hashem gave 39 curses:
10 to the serpent10 to Adam10 to Eve9 to the earth
(Tikkunei Zohar 64-5)
39 was the age at which the Ramchal died (1707-1746).
The categories of work used to build (and use?) the Mishkan (Shabbat 49b)
Also the number of times the Torah uses the words מלאכה, מלאכתו, מלאכת (also Shabbat 49b)