This is the approved revision of this page, as well as being the most recent.
- In a leap year, the 14th and 15th of Adar II is celebrated as Purim, while the 14th and 15th of Adar I are Purim Katan. One can't say Tachanun. fast, or eulogize on Purim Katan. 
- All agree one may eulogize a Talmud Chacham at the Levaya on Purim Katan
- There is no Tachanun on the Mincha the day before Purim Katan. 
- One doesn’t say Al HaNissim on Purim Katan but if one did say it, one doesn’t have to repeat. 
- Some say to increase festivity and to increase in a meal on Purim Katan. 
- It’s permitted to work on Purim Katan. 
- Megilah 6b brings a dispute about which Adar to celebrate Purim. The Rambam (Megilah 1:12), Tur and S”A 697:1 rule that Purim is celebrated in the second Adar.
- Maharil (Beginning of Hilchot Purim) writes that minhag Magensa was to say Tachanun on Purim Katan. However, Sh”t Tashbetz 2:2248 writes that we don’t say Tachanun on Purim Katan. This is also the opinion of S”A 697:1.
- Rosh (Megilah 1:7) says that nowadays fasting and eulogies is permitted on Purim Katan. Sh”T Maharam (Prague 643), Tashbetz 178, Sefer HaParnes 269, Hagahot Maimon (Megilah 2:Shin), Agudah (Megilah 1:6), and Tur 697 hold like the Rosh. However, Rambam (Megilah 2:13) implies that even nowadays one can’t fast or eulogize on Purim Katan. Smag (Asin MeDivrei Sofrim 4), Rabbenu Yerucham 10:1 in name of the Rif, Tosfot (6b s.v. VeRabbi Eliezer), Ran (6b s.v. Elah), Meiri 6b, Shibolei Leket 203, Or Zaruh 2:371, and S”A 697:1 rule like Rambam.
- Torat HaMoadim adds that a Talmud Chacham during the levaya is permitted as it’s even permitted on Chanukah and Purim (S”A Y”D 401:5).
- Mishna Brurah 131:33
- Mishna Brurah 697:1
- Tosfot Megilah 6b s.v. VeRabbi Eliezer says that the Minhag was to increase festivity and to have a meal on Purim Katan but disagrees with it based on the Gemara. Ran 6b, Smak 148:2, Hagahot Maimon (Megilah 2:Shin), Rabbenu Peretz (Hagahot Tashbetz 178) bring the Minhag only on the 14th of the first Adar. Bet Yosef 679 writes that nowadays the minhag isn’t to have a meal on Purim Katan, while, Rama concludes it’s preferable to have a increase a little in a meal to satisfy all opinions. Mishna Brurah 697:5 writes that one should preferably have a small feast which should be in order to give respect to the miracle of purim.
- Rabbenu David Avudraham (Purim pg 208) forbids work on Purim Katan, while Smak 148:2 and Hagahot Maimon (Megilah 2:Shin) permit. Most Achronim rule leniently including Torat HaMoadim 1:8.