The animal on the cover of Learning Domain-Driven Design is a mona monkey (Cer‐ copithecus mona), which can be found in the tropical forests of West Africa and the Caribbean islands, where they were introduced during the slave trade. They leap from trees in the mid- to top canopy, using their long tails for balance.

Mona monkeys have brownish fur that’s darker around their faces, limbs, and on their tails. Their undersides, including the insides of their legs, are white. Females average 16 inches in length while males average 20 inches—and the tails add another 26 inches or more. Long tufts of fur on the cheeks of Mona monkeys can tint yellow or gray, and their noses have some light pink coloring. The cheeks serve as pouches for food as they forage, holding as much as their stomachs can.

Mona monkeys eat fruit, seeds, insects, and leaves and live for about 30 years in the wild. Each day, they forage multiple times in large groups. Packs larger than 40 have been documented; typically a male dominates the group, mating with multiple females and fighting off competing males. These groups can get very noisy.

Mona monkeys have a conservation status of Near Threatened due to human activi‐ ties. Many of the animals on O’Reilly covers are endangered; all of them are impor‐ tant to the world.

The cover illustration is by Karen Montgomery, based on a black and white engraving from Lydekker’s Royal Natural History. The cover fonts are Gilroy Semibold and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.