This issue has variants.
This issue is bannered "Anniversary Celebrating Batman's 600th Appearance in Detective Comics" even though it is actually the 601st appearance in Detective Comics.
This article, appearing on the inside front cover, explains the structure of the issue: a reprint of Batman's first appearance, a reprint of the story Julius Schwartz commissioned to commemorate Batman's thirtieth anniversary, and two new stories using the same plot as the others created by the then-current creative teams of Batman and Detective Comics.
New story, commissioned by Julius Schwartz in celebration of Batman's thirtieth anniversary, which re-uses the plot of "Case of the Chemical Syndicate" from Detective Comics #27. Credits for script, pencils and inks confirmed from Julius Schwartz's editorial records, provided by DC Comics. The original story is 16.67 pages long; this reprint fills in the final 0.33 page with a caption box ("Several significant changes were made, of course...").
New story re-using the plot of "Case of the Chemical Syndicate" from Detective Comics #27. Story is dedicated to "Bob Kane and Bill Finger and all those others who have kept the legend alive."
Promotes the forthcoming series, Angel and the Ape (DC, 1991 series). Appears between pages 15 and 16 of the third story sequence.
Promotes Guy Gardner "solo epic" in Green Lantern (DC, 1990 series) #9-12. Appears immediately following the third story sequence and immediately prior to the Flash promo.
Promoting The Greatest Flash Stories Ever Told (DC, 1991 series) #[nn] with an image very close to the cover art for the hardcover. Appears immediately following the previous sequence and prior to the fourth story sequence.
New story re-using the plot of "Case of the Chemical Syndicate" from Detective Comics #27. The final two-page spread of this story shows Batman swinging above images of his friends and foes with the number 600 super-imposed over the Bat-Signal behind him along with two caption boxes concluding the narration from the story.
Promotes the Venom storyline, beginning in Legends of the Dark Knight (DC, 1989 series) #16. Appears between pages 6 and 7 of the fourth story sequence.
There are a number of advertisements in this issue. The first page of ads contains 20 small ads on a single page prior to page 6 of the first story sequence. Remaining ads promote Capcom's Mega Man 3 for the Nintendo Entertainment System (between pages 1 and 2 of the second story sequence), Fleer's 1991 series of baseball cards (between pages 13 and 14 of the second story sequence), Capcom's Destiny of the Emperor game for Nintendo (between the second and third story sequences), Upper Deck's 1990-91 series of hockey cards(between pages 9 and 10 of the third story sequence), personalized baseball cards from Cracker Jack (between pages 20 and 21 of the fourth story sequence), Buck Rogers XXVc Role-Playing Game and Countdown to Doomsday computer game from TSR (following the fourth story sequence), Great Eastern Conventions comic book convention in February 1991 (following the TSR ad), the Ultimate Game Club phone tipline (top half of last page in issue), the National Baseball Club Hotline (bottom half of final page), and Akklaim's Arch-Rivals: A Basketbrawl, a game for the Nintendo Entertainment System (on the back cover).
This ad for the 3 Musketeers candy bar is in comic form.