Mozart’s organ (or “epistle”) sonatas are some 17 in number and date from his Salzburg years during the 1770s. All of these works are short but not slight, and many aligned to particular mass settings composed during the same years. Enjoying the luxury of a string ensemble as well as organ to compose for in a liturgical setting, these sonatas were part of the structure of the liturgy, dividing the Sunday’s epistle and gospel. Unlike the rest of Mozart’s chamber output, therefore, they are devotional works rather than secular, concert compositions.