The animal on the cover of Parallel and Concurrent Programming in Haskell is a scrawled butterflyfish (Chaetodon meyeri). This fish can grow up to 8 inches in length and is characterized by its white or blue-white body and yellow-edged black bar running through its eyes.

This species of butterflyfish can be found in the Pacific and Indian Oceans, at depths of 2 to 25 meters. Because they generally prefer coral-rich areas, these fish are susceptible to habitat loss. Though there have been no population declines documented to date, this species' food source is live coral and is sensitive to climate-induced coral depletion.

The cover image is of unknown origin. The cover font is Adobe ITC Garamond. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.