Traditional wood adhesive systems used in the production of wood-based composites are commonly made of four major synthetic thermosetting resins, namely phenol-formaldehyde (PF), urea-formaldehyde (UF), melamine-formaldehyde (MF) resins, and pMDI [39; 40; 41]. PF resins, with an approximate annual consumption of up to three million tons [5], are the second most widely used adhesives for wood composites, preceded only by the UF resins. PF resins are typically synthesized under alkaline conditions from the phenol-formaldehyde reaction. They provide high adhesion and mechanical strength [42], temperature stability [43], low starting viscosity, and high water resistance of the cured resins [44; 45]. In exterior-grade products such as the oriented strand board (OSB), softwood plywood, and sidings, which require external exposure durability, these resins are extensively used [23; 40; 46; 47; 48]. UF resins, obtained by the reaction of urea and formaldehyde, are the most predominant synthetic adhesives, used for production of interior-grade wood composites, such as particleboards and medium-density fiberboard (MDF) for furniture and a number of other applications, in which dimensional stability and surface uniformity are critical requirements [49]. UF resins require a shorter pressing time and lower pressing temperature than PF resins, resulting in accelerated performance and relatively low energy use; they are ideal for producing light-colored decorating products [40]. MF resins are usually used for sundry applications, such as paper processing, laminate decoration, and paper coating. Due to the relatively high price of melamine, MF resins are typically mixed with UF resins for particular applications, produced and traded as melamine-urea-formaldehyde (MUF) resins [26]. pMDI adhesives are characterized by quick curing, formaldehyde-free emission characteristics, low loading amounts, and excellent weather resistance; they are mainly used in the production of OSB and other similar particulate wood-based panels [40; 50]. The relatively greater price of pMDI compared to the other common wood adhesives is the main limiting factor for their wider industrial application. Manufacturing of these resins has relied on non-renewable petroleum-based resources [51]. There is also an increased interest towards the development of sustainable, bio-based, \"green\" adhesives from different renewable biomass feedstocks, such as proteins [52; 53; 54; 55; 56], starch [57; 58], tannins [37; 59; 60; 61], and lignin [62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72]. In addition, other biomaterials were utilized in the development of bio-based adhesives, e.g., cashew nutshell liquid (cardanol) [73], vegetable oils [74], fungal mycelium [75], etc. However, most of these raw materials were reported only as conceptual bioadhesives, and no industrial trials have been performed. The production of bio-based adhesives raises additional challenges; adhesives made from renewable natural materials often have low water resistance or are too costly to compete effectively with fossil-derived polymers. The often broad variations in properties due to different growing conditions, source form, growth time, access to nutrients, climate, and other factors, are another challenge when using bio-based polymers. The extraction and fractionation processes that are important for the bio-based polymer isolation would also affect the adhesives' final properties and costs. Therefore, the complete replacement of robust synthetic polymers, having well-known and reproducible characteristics, with fully bio-based polymers as wood adhesives at an industrial scale is challenging [25]. The aim of the present review is to summarize the current state of research and recent developments in the field of lignin- and tannin-based NIPUs for wood adhesives.