Although the German version of The Three Investigators starts with The Secret of Terror Castle, it continues through The Mystery of the Cranky Collector, then picks up with the "Crimebusters" series and continues on with German-language originals from there (starting at number '56'). The German-language originals started in 1993 with books by Brigitte-Johanna Henkel-Waidhofer. She wrote 16 books for Kosmos. After her era ended, several other authors continued to write in the series at the rate of six books per year (in contrast to the U.S. series, which published one new story every year or so after Robert Arthur's death). In Germany, the franchise has also been the source of audioplays, films and graphic novels.

Die drei ??? (The Three Investigators)

The bold numbers in square brackets are the chronological order these take place in the German continuity which includes the original series and Crimebusters. Bold titles mean the episode was also translated into English to serve as a school book. Specials:

Dein Fall! (2012-)

Translates as 'Your Case!', these are Choose Your Own Adventure–style interactive books.

MIDI Format books (2013)

In 2013, Kosmos published a new set of smaller sized books. These perfect-bound paperbacks are written by Christoph Dittert and are 144 pages long, with dimensions 14.4 × 10 cm.

German American-English Series (2005-2011)

In 2005, the German publisher Kosmos started a new series of stories in English, translated from the original German titles. The Three Investigators have their German names in these books, and they are not referred to as "The Three Investigators," but as "Die Drei ???" (literally, "The Three Question Marks"). (Original German titles in italics)

German British-English Pons Die drei ??? Series (2009-2011)

These British-English translations include an abridged version of the original story both in German and English, plus a vocabulary part and grammar exercises. Accompanying the books are CDs containing narrated audio versions of the English texts. These books refer to the protagonists as "The Three Investigators," not "Die drei ???" as in the American-English editions.

Die drei ??? Kids (The Three Investigators Kids) Series (since 1999)

In this series, the Three Investigators are 10 years old, thus making it a kind of prequel to the original series. Their headquarters is a water tank close to Rocky Beach nicknamed "Coffee Pot", which was once used to fill up locomotives. Joining the recurring cast are Mr. Porter, Rocky Beach's general dealer, Harbor Master Ernesto Porto, and Giovanni, who runs an ice cream parlor. Another difference to the original series is that Bud Norris, Skinner's father, operates a shady bar in the city center.