Bad Boy Records / Puff Daddy aka P. Diddy
Pac hated Puffy mainly because he was with Biggie, was competition to Death Row. Death Row were planning to form Death Row East and have the whole Rap Game under their influence but Puffy was direct opposition to this. At an industry awards ceremony Suge Knight summed up the Puffy situation perfectly when he said "If anyone wants to come to a record company were they don't want the executive producer dancing, singing all up in the videos come to Death Row." Puffy used his other artists to promote himself. Puffy didn't write his own lyrics, his flow was weak and his beats were ripped.
Pac also says that Puffy was involved in the NY shooting at settin' him up because Puffy's company was meant to be financed by the people who shoot him and Pac was carrying a gun at the time so if he pulled it out he would get shot so they made it look like a jewelry robbery.

Lil' Kim once said that Bad Boy did a track dissing Tupac but they didn't released it after Tupac "died". The song did not feature Biggie; it was only Lil' Kim and Junior M.A.F.I.A.
Lil Kim

Dr. Dre
This all began when Snoop was on trial for murder. One of the witnesses said that Dre was in the car and if he had appeared at court he could have testified but he said that he was too busy. This pissed 2Pac off because he thought that Dre wasn't showing loyalty to his homeboy Snoop and to Death Row. He was also pissed off because Dre had never really done anything since The Chronic and was still earning a heap of cash off Death Row. Then because one minute Dre was sayin' that he was all Gangsta and that and the next he was sayin' the opposite. 2Pac also said that he got Dre kicked outta Death Row but Dre said that he wasn't happy with the violent culture that surrounded Death Row and that at one point someone was beaten up for rewinding a tape too far. In the song "Toss It Up" 2Pac calls Dre gay and he does the same in "To Live & Die In L.A.". But Dre said in "The Up In Smoke Tour" of 2000 that it was a pleasure to work with 2Pac. He also says Dre cheated on his wife "What's down in the darkness, will come to light".

Mobb Deep
Before Pac was sent to jail he did an article in Vibe talking about "Thug Life". While he was in prison he heard Mob Deep on the radio sayin' "Thug Life, We Still Livin' It." So Pac sent out some of his homies to a Mob Deep concert and start screaming out "Thug Life" but they didn't acknowledge this so 2Pac took this as an insult. Mob Deep think they is it on record but they don't have the balls to say it off record. 2Pac didn't even consider Mob Deep to be on the same level as far as he was concerned he was on a Higher Level than them. He even dissed them because one of them has sickle cell. Mob Deep retaliated with "Drop a Gem on Em."

Nas
I am not sure how this rivalry started but on The 7 Day Theory at the beginning in Bomb First (My Second Reply) 2Pac identifies Nas as the ring leader in an attempt to assinate 2Pac. Nas totally bites 2Pac in the way he raps and he portrays himself out to be a Thug just like 2Pac. Nas saying how he got shot just like 2Pac and in the video for "Hate Me Now" him and Puffy are totally disrespecting Pac by being Crucified at the beginning just like the cover of The 7 Day Theory, they also dress like 2Pac did and pour out the liquor like Pac and Dre did on the California Love Remix. Nas used to diss 2Pac all of the time but since he has died Nas has showed Tupac respect in his interviews.

Chino XL
This all began when Chino said that 2Pac was raped in jail. 2Pac dissed him a bit in Hit 'Em Up bit not much because he felt that he wasn't important enough and dissing him would only pump him up. I have never have heard of any CD's or out being released by him.

Wendy Williams
Wendy Williams said that 2Pac got raped in jail. Well if u have ever heard the unreleased song "Why U Turn On Me?" does he stick it to her or what. All of the way through the songs he calls her sayin' she has a fat arse and should go to a fat farm.

LL Cool J
This all started when Biggie had a song called "Who Shot Ya?" and LL came out with "I Shot Ya". LL disses everyone because he thinks that he is the best rapper ever. 2Pac never gave LL any reason to diss him and even praised him in "Old School." 2Pac retaliated with "L'il Homies."

Jay-Z
This all began when Jay-Z appeared on a song "New York's Finest" with Biggie which dissed 2Pac. Jay-Z was close to Biggie and appeared on many Bad Boy albums. 2Pac replied by dissing Jay-Z on "Bomb First (My Second Reply)," "Against All Odds" and "All Out." Even though they were enemies at some award show when Jay-Z got his award he said "2Pac 4 Eva" which showed he really liked Pac.

Dan Quayle
This all began when Dan Quayle was Vice-President and during an election campaign gave a speech saying "2acalypse Now" had no place in society. During all of his cases and trouble at that time 2Pac said Dan Quayle was the thing that bothered him the most and he disses him on his next album "Strictly 4 My N.I.G.G.A.Z."

The Fugees
The Fugees began dissing 2Pac in interviews. Wyclef started it by speaking all downward about 2Pac then the other two began to diss him as well. As far as I know 2Pac never gave them any reason to diss him. 2Pac retaliated with the unreleased song "When We Ride Our Enemies."

C Delores Tucker
C Delores Tuck filed a $10 million Law Suit against 2Pac because she said his lyrics on "All Eyez On Me" She also said 2Pac's music was pornographic smut. 2Pac mentioned her on "Picture Me Rollin" and "Wonder Why They Call U Bytch" and dissed her on "How Do U Want It."