Hal Abelson gives an introduction to the "Structure and Interpretation of Computer Programs" lecture with an explanation of Declarative and Imperative programming.

Excerpted and adapted from Hal Abelson, "Introductory Undergraduate Subjects in Computer Science":-

6.001 differs from typical introductory computer science subjects in using Scheme (a block-structured dialect of Lisp) rather than Pascal as its programming vehicle. The subject's developers feel strongly that Pascal is hopelessly constraining, and that important ideas (such as functional programming and object-oriented programming) can be addressed within Pascal only awkwardly, if at all. In addition, they consider top-down hierarchical design, so often emphasized as a central theme in computer programming subjects, to be a minor and relatively simplistic strategy in the programmer's arsenal for attacking complex problems.

http://mitpress.mit.edu/sicp/course.html (less)