The first series ran for 47 issues, from February 1977 to October 1984. A special Iron Man issue appeared in 1988, followed by a more ambitious (and successful) second volume that lasted for 114 issues between July 1989 and November 1998.
The What If? storylines consisted of:
#1 - What if Spider-Man joined the Fantastic Four?
#2 - What if the Hulk had the brain of Bruce Banner?
#3 - What if the Avengers had never been?
#4 - What if the Invaders stayed together after World War II?
#5 - What if Captain America hadn't vanished during World War II?
#6 - What if the Fantastic Four had different super-powers?
#7 - What if someone else besides Spider-Man had been bitten by the radioactive spider?
#8 - What if the world knew Daredevil was blind?
#9 - What if the Avengers fought evil in the 1950s?
#10 - What if Jane Foster had found the hammer of Thor?
#11 - What if the original Marvel Bullpen had become the Fantastic Four?
#12 - What if Rick Jones had become the Hulk?
#13 - What if Conan the Barbarian walked the earth today?
#14 - What if Sgt. Fury had fought World War 2 in outer space?
#15 - What if Nova had been four other people?
#16 - What if Shang-Chi, Master of Kung Fu, fought on the side of Fu Manchu?
#17 - What if Ghost Rider, Spider-Woman, Captain Marvel were villains?
#18 - What if Dr. Strange were a disciple of Dormammu?
#19 - What if Spider-Man had never become a crimefighter?
#20 - What if the Avengers fought the Kree-Skrull War without Rick Jones?
#21 - What if Invisible Girl of the Fantastic Four married the Sub-Mariner?
#22 - What if Dr. Doom had become a hero?
#23 - What if the Hulk had become a barbarian?
#24 - What if Gwen Stacy had lived?
#25 - What if Thor and the Avengers fought the gods?
#26 - What if Captain America had been elected president?
#27 - What if Phoenix had not died?
#28 - What if Daredevil became an agent of S.H.I.E.L.D.?
#29 - What if the Avengers defeated everybody?
#30 - What if Spider-Man's clone lived?
#31 - What if Wolverine had killed the Hulk?
#32 - What if the Avengers had become pawns of Korvac?
#33 - What if Dazzler had become the herald of Galactus?/What if Iron Man was trapped in the time of King Arthur?
#34 - Humor issue (various)
#35 - What if Elektra had lived?
#36 - What if the Fantastic Four had not gained their super-powers?
#37 - What if the Beast and the Thing continued to mutate?
#38 - What if featuring Daredevil and Captain America
#39 - What if Thor battled Conan the Barbarian?
#40 - What if Dr. Strange had not become master of the mystic arts?
#41 - What if Sub-Mariner had saved Atlantis from its... Destiny?
#42 - What if the Invisible Girl had died in Childbirth?
#43 - What if Conan the Barbarian was stranded in the 20th century?
#44 - What if Captain America were revived today?
#45 - What if the Hulk went berserk?
#46 - What if Spider-Man's Uncle Ben had lived?
#47 - What if Loki had found the hammer of Thor?