Osteoarthritis is a major health problem and obesity is one of the most important risk factors. This book describes research on the possible pathophysiology of osteoarthritis due to excess of fat tissue: do metabolic factors play a role? and what will happen to osteoarthritis progression when obesity is present together with another important risk factor (i.e. joint malalignment)? Moreover, other hot topics in osteoarthritis research are discussed, such as: which structures cause pain in knee osteoarthritis? and what are the risk factors to have worsening of lower limb osteoarthritis?