Trees are essential to life. Their tall, large structures are supported by a recalcitrant substance called lignocellulose, made up of complex and large molecules consisting of polysaccharide and lignin, which are assembled and form a 3D network. My investigations concern the molecular structure and formation of lignocellulose in wood cell walls. Fungi have a deep association with trees. Wood-rotting fungi have an ability to degrade wood. How they “eat” wood is the other question. To explore these areas, I work on the development of analytical methods using nuclear magnetic resonance and mass spectroscopy. Trees can be used not only for wooden buildings and products but also for chemicals and energy. Thus, learning from nature and converting lignocellulose in an environmentally friendly system, trees and fungi would help to promote a sustainable future.