Monk straps are a classic design that is thought to stem from the shoes that monks would wear around the monasteries all the way back in the middle ages. Today the structure is much more advanced than the simple sandal-like versions the monks wore. Read more about the history of the monk strap shoe here.
The Monk strap shoe lands somewhere between a derby and oxford in terms of formality. They look greatest when worn with more formal attire, such as suits, but can do well with a well-coordinated, relaxed outfit.