Here it brings the following sources on the matter:
The Chasam Sofer (Shut Y.D. 341) was concerned about it and spoke about pushing off the learning until the coming Tisha B'Av.
Sefer Chassidim (261) is an interesting source. He says you should learn them because they aren't learned generally. So there you have the existing practice of not learning them ...
Several events are listed in chapter 13 of Megilat Ta'anit:
The Jews in the wilderness were decreed to die in the wilderness and not enter Israel.
The First Temple was destroyed.
The Second Temple was destroyed.
The city of Beitar was conquered.
The City was razed.
בתשעה באב נגזר על אבותינו שלא יכנסו לארץ וחרב הבית בראשונה ובשניה
נלכדה ביתר ונחרשה העיר
Not words of comfort
In Pirkei Avot 4:181, R' Shim'on ben Elazar says:
וְאַל תְּנַחֲמֶנּוּ בְּשָׁעָה שֶׁמֵּתוֹ מֻטָּל לְפָנָיו
[D]o not console him at the time when his deceased lies before him;
The Rambam, in Hilchot De'ot 5:7, includes this rule in his advice for Torah scholars as a special case of
אִם רוֹאֶה שֶׁדְּבָרָיו מוֹעִילִים וְנִשְׁמָעִים אוֹמֵר ...
Here are additional events to the ones already noted in other answers
Expulsion from England (1290): The Jews of England were expelled by King Edward I (chabad.org)
French expulsion (1306): The Jews were expelled from France (from here)
Spanish Expulsion (1492): The Jews of Spain were expelled by King Ferdinand and Queen Isabella on the 9th of Av of 1492, ...
Rav Shumel Kamentzky, cited in sefer Kovetz Halachos pg 231, writes that a nursing woman or someone riding a bus may sit, because it is a necessary thing and not done out of enjoyment.
Sitting on the toilet is a need and not meant for enjoyment and should be the same.
When I was an aveil (for each of my parents), I changed my seat for the entire year. That is also the general minhag in my shul. This included Shabbosa as my new seat became my makom kavua for that year. After the year I returned to my normal seat.
Our shul is somewhat "Yeshivish" on the East coast of the United States (Baltimore). I consider us somewhat to ...
Shulchan Arukh YD 340:14
על כל המתים אם בא להחליף תוך ז' ימים מחליף ואינו קורע על אביו ואמו אם מחליף תוך ז' קורע כל הבגדים שהוא מחליף ואינו מאחה לעולם כמו בפעם הראשון.
Upon any [ordinary] death, if [the mourner] comes to change [his clothes] during Shiva, he may switch and not tear [again], [but] on one's father and mother, if he switches [clothes] ...
The idea behind not learning the laws of mourning, is a superstition that this could cause someone to die, and the laws to become applied (see Hattam Sofer YD 346, and a discussion of the idea here). R. Elyashiv is quoted as rejecting this idea here. Similarly, this article quotes Yossef Omets (pg. 270) as referencing this superstition, but nevertheless ...
Zvi Ron wrote an entire article about this in Ḥakirah (vol. 13).
To quote and summarize: the earliest source is the Hattam Soffer (19th century) [i]:
He explains that mirrors were turned around to face
the wall based on the mourning practice of kefiat hamittah, overturning the beds. The Babylonian Talmud (Mo‘ed Katan
15b) gives ...
See Yevamot 62b. The juxtaposition of the sentences in Gemara leads to understand that he learned this from a verse (Ecclesiastes 11.6).
ר"ע אומר למד תורה בילדותו ילמוד תורה בזקנותו היו לו תלמידים בילדותו יהיו לו תלמידים בזקנותו שנא' בבקר זרע את זרעך וגו' אמרו שנים עשר אלף זוגים תלמידים היו לו לרבי עקיבא מגבת עד אנטיפרס וכולן מתו בפרק אחד מפני שלא נהגו ...
Rashi on 21b points to the continuation of the gemara on Moed Katan 23a which provides the answer
ואם אין לו בנים מותר לישא לאלתר משום ביטול פריה ורביה הניחה לו בנים
קטנים מותר לישא לאלתר מפני פרנסתן
And if he does not have children, he is permitted to marry another
wife immediately due to the need to not neglect the mitzva to be
fruitful and ...
From "The Jewish Way in Death and Mourning" by Maurice Lamm:
Community business meetings, such as synagogue or fraternal
organization membership meetings, are permitted the mourner after
Social dinners, even though no music is played, and even though they
are held for charitable causes, are not to be attended by mourners for
It is Halacha and is brought in Shulchan Arukh YD 384.
It applies on Shabbat just like all other mourning restrictions: only when not done publicly. So learning Gemara in your house is prohibited, but getting an Aliyah that you get every week and people would notice your not getting is permitted. (YD 400)
Heinrich Himmler received the formal command from the Nazi Party to initiate the Final Solution, an order which resulted in millions of Jewish deaths. This happened on Tisha B'Av in 5701, which corresponds to August 2, 1941 on the Gregorian calendar. (Source)
Rav Moshe Feinstein (Igrot Moshe YD 4:61:4) ruled they should not split up because of BeRov Am, and all the more so in a case where the extra group would not be in a Shul or even a room without a Torah scroll.
Rav Chaim Kanievsky (Gam Ani Odekha (Shonim) 3:34) says it is better in your situation not to split up into multiple Minyanim.
Rav Yehuda Herzl ...
Nitei Gavriel Aveilus 56-58 discusses the different Minhagim. This is my understanding of what he says.
An Aveil should not Daven for the Amud on Shabbos, Yom Tov, and the high holy days. Exceptions are as follows. If there is no one who can Daven as good as the Aveil the Aveil may Daven during these days. In addition if the Aveil is the regular Chazan on ...
Nitei Gavriel Aveilus2 23:20 says that the father of the baby can participate in a Bris and Seuda for his son even during the Sheloshim.
אבי הבן, כשהוא אבל עושה משתה ושמחה ביום המילה ומשתתף אף בתוך שלשים
In the notes he mentions the Shach Yoreh Deah 394:2 quoting the Derisha in the name of the Rokeach that one should not make a Simcha and party on the ...
Rule #1: Don't fight about it.
First, one should never get into fights with others to do Mitzvot (Mishna Berura 53 sk 65). Regarding our case, the Chatam Sofer (YD 345) writes that if you deserve a certain spot and someone else takes it, he hasn't gained anything and you haven't lost anything (ie. you get the "credit" anyway). Plus fighting another Jew ...
Rabbi Oshinski in his sefer Hilchos Aveilus (Perek 3:24) he writes (bringing the Zichron Eliyahu and the Pnei Baruch) that mirrors are covered and some hold that pictures are covered as well. He does note from others that covering picture may only be an issue when people are praying the shmoneh esrei.
Text of sefer:
There is an opinion that a mourner can be called up to the Torah on a weekday - (but not at all on Shabbat). It's the opinion of the Maharil in Hilchot Kriat HaTorah (דף ק"ח סוף ע"א).
He is quoted by the Bach on the Tur Yoreh De'ah 384 and by the Prisha (ג) and Drisha [א] in Yoreh De'ah 400.
However, he is quoted as a singular opinion that nobody else ...
Upon hearing bad news, one says the blessing ברוך אתה יקוק אלוקינו מלך העולם דיין האמת"" (OC 222:2).
Regarding mourning, the Shulchan Arukh rules (YD 374.6):
כל מי שמתאבל עליו מתאבל עמו אם מת לו מת ודוקא בעודו בפניו אבל שלא בפניו אין צריך לנהוג אבלות...: הגה וי"א דהאידנא נוהגין להקל באבילות זה של המתאבלים עמו דאין זה אלא משום כבוד המתאבלים ...
When I was a student at Yeshivat Har Etzion, R' Binyamin Tabory gave a Shi'ur on Ma'aseh Rav, based on the Rav's teachings and Minhagim. When he discussed Sefirah, the Three Weeks, etc., he said that if, hypothetically, one could go to a movie at all (which he did not feel was so simple, for reasons relating to issues of modesty - he said he once went to a ...
No, Rav Shmuel Kamenetsky in sefer Kovetz Halchos 232:13 that saying "shalom" is forbidden but to say "see you later" or "good night" before one goes to sleep is not a problem, but "good morning" is. See footnotes in the book if you have access to it.
The Nishmas Avraham (Chelek Daled Siman 42) discusses this. An adopted child is obligated to honor his adoptive parents in order to express gratitude for the kindness they did for him, but does not have the the actual mitzvah of honoring parents. He should say kadish for them but not at the expense of the biological children. He is not obligated to tear ...
R. Yitzchak Abadi discusses this in a responsum:
Ohr Yitzchak 1:219
ואגב דעסקינן ברחיצה לא אוכל להתאפק מלהעיר על מנהג של הרבה אנשים אשר לא
מתרחצים מר"ח אב עד העשירי בו וחושבים שלרחוץ הוא איסור גמור וגורמים בזה
לנזקי שכנים וחלול ה' העולה על כולנה כי למרבה הצער בימים אלה החום גובר
והזיעה מתרבה והריח נודף וא"א לעמוד גם מחוץ לד' אמותיהם ולפעמים מתכנסים
As DoubleAA pointed out, the Beis Yosef quotes the "Gaonim".
Those "Gaonim" could be referring to the Halachos Pesukos, which was a sefer written by one of the Gaonim, possible Rabbi Yehudai Gaon.
וששאלתם למה אין מקדשין ואין כונסין בין פסח לעצרת אם מחמת איסור ואם לאו הוו ידעין שלא משום איסור נגעו בה אלא משום מנהג אבילות שכך ...