| Issue | #40 |
| Published | January 1968 |
| Cover Price | 0.12 |
| Pages | 36 |
| Editing | Stan Lee |
| Characters | The X-Men (Angel, Beast, Cyclops, Iceman, Marvel Girl); The Frankenstein Android |
| Genre | superhero |
| Pencils | George Tuska |
| Inks | George Tuska |
| Reprinted | in X-Men (Marvel, 1963 series) #88; in X-Men: First Class Giant-Size Special (Marvel, 2008 series) #1 |
| Characters | The X-Men (Angel, Beast, Cyclops, Iceman, Marvel Girl); I: The Frankenstein Android (I, D; not the Frankenstein Monster); Changeling |
| Genre | superhero |
| Script | Roy Thomas |
| Pencils | Don Heck |
| Inks | George Tuska |
| Letters | Artie Simek |
| Notes | Professor X secretly replaced by Changeling through issue #43. |
| Reprinted | in X-Men (Marvel, 1963 series) #88; in Marvel Special (Marvel Italia, 1994 series) #14; in X-Men: First Class Giant-Size Special (Marvel, 2008 series) #1 |
| Characters | O: Cyclops (continued); V: Jack O'Diamonds; |
| Genre | superhero |
| Script | Roy Thomas |
| Pencils | Werner Roth |
| Inks | John Verpoorten |
| Letters | Al Kurzrok |
| Reprinted | in Amazing Adventures (Marvel, 1979 series) #3 (February 1980); in Marvel Special (Marvel Italia, 1994 series) #4 |