Mario Herrera has a Degree in Education and an MA in EFL. From young children to adults, Mario has taught English for more than 30 years at all levels. Author and co-author of many acclaimed ESL/EFL series that are used in levels ranging from pre-primary to junior high schools, he is also an international consultant and teacher trainer. Mario travels the globe, directing seminars and delivering professional development workshops throughout the Americas, Europe, the Middle East, and Asia.

Christopher Sol Cruz has been involved in the field of English language instruction and materials writing since 1988. Sol Cruz is the co-author of the primary EFL series Big English, as well as writing and developing numerous English learning materials for a variety of age groups in Latin America, Asia, the Middle East, and the US. In addition to writing, Sol Cruz has given academic presentations and run teacher professional development workshops around the world, and is an avid language student.