In the 20th century, the composite materials with polymer matrices, i.e. polymer matrix composites (PMC), became the engineering structural materials of choice because of low cost, ease of processing, weigh savings, corrosion resistance and other major advances. The PMC are used in automotive and aeronautical industry, bridge structures, water and waste systems and more recently in the offshore exploration and oil production. Prevailing use of PMC is stipulated by high specific characteristics, a possibility of properties modification matching the matrices and fillers, and their relative content. The book is based on the research results obtained in the time period of 1990-2010 at the Laboratory of Long-Term Deformation, in the Institute of Polymer Mechanics, Riga, Latvia. This book examines the results of experimental investigations of present-day composite materials.