There are a number of books related to artificial life:

Free Books

Conway’s Game of Life: Mathematics and Construction by Nathanial Johnston and Dave Greene

Biological Bits by Alan Dorin

Rise of the Self-Replicators by Tim Taylor and Alan Dorin

Non-technical Books

Artificial Life: The Quest for a New Creation by Steven Levy

The philosophy of artificial life edited by Margaret A. Boden

Complexity: A Guided Tour by Melanie Mitchell

The Computational Beauty of Nature: Computer Explorations of Fractals, Chaos, Complex Systems, and Adaptation by Gary William Flake

Textbooks

Introduction to Artificial Life by Christoph Adami

Citations

Flake, G. W. (2008). The computational beauty of nature: computer explorations of fractals, chaos, complex systems, and adaptation (9. print). The MIT Press.
Mitchell, M. (2011). Complexity: a guided tour (1. iss. as an paperback). Oxford University Press.
Boden, M. A. (Ed.). (1996). The philosophy of artificial life. Oxford University Press.
Levy, S. (1992). Artificial life: the quest for a new creation (1st ed). Pantheon Books.
Adami, C. (1998). Introduction to artificial life. Springer.