This book is about graduation project of three students (Faculty of engineering, Alexandria university), It is describing the principles of diving techniques, under water wet welding and dry welding also the experiments done by them and the results & conclusions of their experiments. Any one interested on under water welding or offshore oil and gas industry this book will be helpful for his knowledge. Underwater Wet and dry welding is a specialty because it is combination between the restrictions of working under water and welding complexity. This book will be a great support for any one looking for information about under water welding and offshore diving.