Abstract: For developing novel fully biological materials, a central question is how we can utilize natural components in combination with biomimetic strategies in ways that both allow feasible processing and high performance. Within this development, adhesives play a central role. Here, we have combined two of nature’s excellent materials, silk and cellulose, to function as an adhesive system. As an initial step in processing, wood was delignified. Without lignin, the essential microstructure and alignment of the wood remain, giving a strong scaffold that is versatile to process further. A recombinant spider silk protein was used as a fully biological and water-based adhesive. The adhesive strength was excellent with an average value of 6.7 MPa, with a maximum value of up to 10 MPa. Samples of different strengths showed characteristic features, with high tear-outs for weaker samples and only little tear-out for strong samples. As references, bovine serum albumin and starch were used. Based on the combined data, we propose an overall model for the system and highlight how multiple variables affect performance. Adhesives, in particular, biobased ones, must be developed to be compatible with the overall adherend system for suitable infiltration and so that their mechanical properties match the adherend. The engineering of proteins gives an unmatched potential for designing adhesive systems that additionally have desired properties such as being fully water-based, biologically produced, and renewable.