The objectives of this research were (i) to obtain a comprehensive description of the surface chemistry of cellulosic fibres by thermodynamic and spectroscopic methods, (ii) to use this description to clarify the effect of kraft cooking as well as ECF and TCF bleaching on the surface chemical and adhesive properties of cellulosic fibres, (iii) to clarify and understand the connection between the fibre surface properties and some key sheet properties (e.g. tensile strength). The charge, surface energy and hydrophobic material in the surface of cellulosic fibres (mainly pine, Pinus sylvestr is and birch, Betula verrucosa) were studied by potentiometric titration, determination of polyelectrolyte adsorption isotherms, determination of contact angles of single fibers and ESCA. Lignin (remnants of middle lamellae or reprecipitated during cooking) is enriched in the surface of unbleached kraft pulp fibres. The fraction of surface lignin removed by oxygen or hydrogen peroxide is much smaller than the total decrease in lignin content. Ozone removes both bulk and surface lignin, while the effect of chlorine dioxide depends on the number of treatments. The low reactivity of surface lignin is due to condensed lignin structures and/orto lignin-carbohydrate complexes.