In today’s increasingly technology-dependent world, mobile applications are becoming more pervasive, impacting educational practices across learning contexts, and subsequently changing the landscape of education. This paper focuses on the pedagogical foundations informing the design of a mobile application (app) crossword puzzle developed for teaching vocabulary to students of a second language. The crossword puzzle app is inherently game-based, making the learning process more appealing to students as an aid in the effective acquisition of vocabulary. It offers a degree of challenge, motivating students to try to solve the puzzle, but also aims to make vocabulary acquisition more exciting and rewarding. It provides an opportunity for students to practice and repeat the sentence patterns and vocabulary, which in turn, assists in the improvement of students’ performance in language acquisition. From a pedagogical perspective, evaluating choices, making inferences, and drawing conclusions are key skills essential for completing crossword puzzles. As a mobile application for smart phones and tablets, the advantages of crossword puzzles are ubiquitous and can be within an arm’s length of most students, and running on a device and in an environment for which most students greatly value.