Spermatozoa are the motile haploid cells that are the male gametes. A spermatozoon fuses with a haploid egg cell to form a zygote. Spermatozoa accounts for nearly half of the genetic material of the diploid offspring. There are two types of sperm cells: one bearing an X chromosome and another bearing a Y chromosome. The sex of the offspring is also determined by the sperm cells. The fusion of the sperm cell having an X chromosome will lead to a female (XX) offspring, while the fusion of the sperm cell having a Y chromosome will lead to a male offspring (XY). A sperm cell has four parts: a head, neck, middle piece and a tail. This book attempts to understand the biology, function and chromosomal abnormalities of spermatozoa. It presents researches and studies performed by experts across the globe. This book will serve as a reference to a broad spectrum of readers.