The objective of this chapter is to provide an overview of novel non-destructive testing methodologies for bonding quality assessment in glued laminated timber developed within a recently completed Swiss National Science Foundation research project (Sanabria, 2012). The focus is set on air-coupled ultrasound testing, which has previously been applied to wood-based panels typically up to 50 mm thick. A novel prototype capable of transmitting ultrasound signals through up to 500 mm thick glulam was developed. A computerized-scanning system allowed imaging of the position and geometry of defects within the bonding planes. A normal transmission setup allows a global assessment of defective bonding planes stacks. Latest results are as well shown for a recently patented slanted lateral transmission setup, which allows separate assessment of individual bonding planes with unlimited beam height and length. The investigations allowed an improved understanding of the wave propagation phenomena in thick laminated timber components through both analytical calculations and finite-difference numerical simulations. An overview of the main findings is as well provided. Future research is planned to combine the developed theoretical and experimental tools in a tomographic inspection method.