Abstract
Macrophages of the body represent a widely dispersed, versatile, and highly responsive homeostatic and defense system. They contribute to innate as well as adaptive immunity to infection, mediating trophic as well as injurious interactions with their local and systemic environment. The concept of macrophage activation has evolved over recent decades, from relatively simple paradigms to bewildering complexity. This chapter will review the background to present understanding of alternative activation of macrophages, consider its relevance to health and disease, and suggest questions for future studies.