My encyclopedia entry **Perturbation Theory** (co-authored with Rob Corless) will soon appear in the **Sage Encyclopedia of Theory**.

**Title:**

Perturbation Theory

**Authors:**

Nicolas Fillion

**Volume:**

The Sage Encyclopedia of Theory, J. Mattingly (Ed.), Sage, forthcoming.

#### Additional information

**Abstract: **This article aims to explain essential elements of perturbation theory and their conceptual underpinnings. It is not meant as a summary of popular perturbation methods, though some illustrative examples are given to underline the main methodological insights and concerns.

Download the PDF of the paper.

Cite as (APA format):

Fillion, N. & Corless R.M. (forthcoming). Perturbation Theory, in: *The Sage Encyclopedia of Theory*, J. Mattingly (ed.), Sage.