The Interpretation of Ecological Data: A Primer on Classification and Ordination

Many multivariate statistical books emphasize calculations and examples, withour providing much understanding of the linear algebra underneath, and many others are high-level mathematics texts. Striking the right balance is difficult. In my experience, Pielou's book is the best in this sense. If you would like to get an entry-level understanding of what classification and ordination methods do, I mean, the maths behind, without getting all the way into proving theorems, this is a great book.