Whether this fast is maintained during times of peace, and times when the Jews have their sovereignty: Rosh HaShanah 18b-19b
Fasting on the 9th of Av was never abolished, even in good times, because its tragedies were "doubled": Rosh HaShanah 18b
Special Rules for Fasting on the 9th of Av
Oppressions of the 9th of Av: Taanit 30a, 30b
Eating/Drinking on the 9th of Av is compared to eating/drinking on Yom Kippur: Taanit 30b
Fate of one who eats/drinks on the 9th of Av: Taanit 30b
Eating during Sunset: Pesachim 54b
When to keep the fast, if it falls out on Friday: Eruvin 40b-41b
When to keep the fast, if it falls out on Shabbat: Eruvin 40b-41b; Taanit 29b; Megillah 5a [2x]; 5b
When to keep the fast, if it falls out on Sunday: Eruvin 40b-41b; Taanit 29b
Keeping an extra day for calendar error: Pesachim 54b
Pregnant and Nursing Women: Pesachim 54b
General Behavior
Learning Torah: Taanit 30a
Teaching Torah to children: Taanit 30a
Learning a Torah topic which one isn't used to, and therefore finds difficult: Taanit 30a
Learning sections of Torah on mourning and punishment: Taanit 30a Doing Work: Berachot 17b; Pesachim 54b; Taanit 30b; Megillah 22b Torah Scholars doing work: Berachot 17b, Pesachim 54b, Taanit 30b
Fate of one who works on the 9th of Av: Taanit 30b
Placing a finger in water: Pesachim 54b
Going to the Ritual Bath, for Immersion which is a Mitzvah: Shabbat 111a
Flipping over the beds and sleeping on the floor: Taanit 26b
Flipping over beds which aren't being slept in: Taanit 30b
Pregnant and Nursing women sleeping on beds: Taanit 30b