This article discusses the classification of the attachment and joining methods in plastics, including mechanical fastening, adhesive bonding, solvent bonding, and welding. It describes the mechanical fastening techniques used to join both similar and dissimilar materials with machine screws or bolts, nuts and washers, molded-in threads, self-threading screws, rivets, spring-steel fasteners, press fits, and snap fits. The article explains solvent bonding used for thermoplastic parts, and tabulates the solvent types used with various plastics. It also describes the surface preparation of plastics, chemical treatment for adhesion, and tabulates the adhesive types for bonding plastics to plastics and plastics to nonplastics. The article briefly describes the welding processes of thermoplastics, including fusion welding (hot-tool, hot gas, extrusion, and focused infrared), friction welding (vibration, spin, and ultrasonic), and electromagnetic welding (resistance, induction, dielectric, and microwave). It concludes with the evaluation of welds using destructive and nondestructive testing.