Genetics plays a major role as an attribute factor in rheumatoid arthritis development. Rheumatoid arthritis (RA) is one of the most common autoimmune diseases affecting up to 2 percent of the world’s population. Loss of self-tolerance in the host immune system has led to this autoimmunity, multifactorial in origin, with a combination of environmental and genetic factors. Numerous susceptibility genes have been identified that predispose individuals to rheumatoid arthritis. The role of putative causal genes with genetic variations in rheumatoid arthritis differ in populations according to their genetic make-up. Interestingly, the genetic entities in rheumatoid arthritis are also involve in a shared molecular pathway in schizophrenia, either conferring as opposing or mutual effect to both complex diseases. The purpose of this book is to provide information on genetic attribute factors in rheumatoid arthritis pathophysiology.