Interpenetrating polymer networks, IPNs, are combinations of two polymers in network form, synthesized and/or crosslinked in the immediate presence of each other. Different kinds of IPNs include the sequential, simultaneous, latex, thermoplastic and gradient types, each with a specific mode. IPNs have been in use since 1914 but have only been researched as a well-defined subject area since the early 1970's. Today, they are researched and used worldwide. This book is a collection of papers from around the world covering the broad areas of basic and applied research on IPNs with several mentions of applications.