This book is an overview of ESIS Technical Committee 4''s activities since the mid-1980s. A wide range of tests is described and the numerous authors is a reflection of the wide and enthusiastic support we have had. With the establishment of the Technical Committee 4, two major areas were identified as appropriate for the activity. Firstly there was an urgent need for standard, fracture mechanics based, test methods to be designed for polymers and composites. A good deal of academic work had been done, but the usefulness to industry was limited by the lack of agreed standards. Secondly there was a perceived need to explore the use of such data in the design of plastic parts. Some modest efforts were made in early meetings to explore this, but little progress was made. In contrast things moved along briskly in the standards work and this has dominated the activity for the last fourteen years. The design issue remains a future goal.