In the Doctoral thesis „Modification of wood bark with nitrogen-containing functions”, as the object of the study, bark of tree species that are most widespread in Latvia (pine, spruce, aspen, black alder and grey alder) has been chosen, which, in modification reactions, demonstrates an enhanced ability to bind nitrogen that is determined mainly by the high content of lignin in bark with active OH groups, as well as the presence of other phenol type compounds. It would be more appropriate to distinguish high-molecular polyphenol compounds in a special group. The chemical composition of the bark of the trees, most widespread in Latvia, has been investigated. For the first time, lignin was modified in bark, not isolating it from the lignocellulose complex. Modification in situ by two different modification methods makes it possible to obtain nitrogen-containing bark derivatives with new, practically applicable properties: for the development of environmentally friendly composite materials – the advantages of the modified bark for use in secondary polymeric systems and for uptake of heavy metals from heavy metal - containing systems are shown. The desoxyamination reaction with diethylepoxypropylamine (DEEPA) enables the introduction of tertiary diethyl amine groups in bark. Different amination regimes were tested and the most suitable one was chosen, in which the active component DEEPA was taken in excess: 1 g bark : 1.5 ml DEEPA : 15 ml H2O, at 98°C and treatment time 1 h. In pine and black alder bark, the highest N content was introduced, namely, 3.84 and 3.58 %, repectively, with a high yield of the product, namely, 135 % and 134 %, respectively. In oxyammonolysis reactions, using ammonium persulphate (NH4)2S2O8 as an oxidiser, it was possible to introduce a high content of nitrogen in pine and black alder bark: 14.32 % and 11.85 %, but the yields of the obtained polymer were relatively low. The modified bark material contains nitrogen in the easy-to-uptake form: the bark mulch can be used as a soil structure forming agent and soil conditioner and, at the same time, as bio-fertiliser (as a result of biodegradtion, the content of humus in soil increases). The Doctoral thesis is written in Latvian, its volume is 129 pages. The thesis contains 48 figures, 32 tables, 4 appendices, and 129 literature references are used there. The work has been elaborated from 2006 to 2012 at the Latvian State Institute of Wood Chemistry in cooperation with the Riga Technical University. 26 articles are published on the results, as well as 12 popular-science articles; presentations are made at 14 international conferences, where 6 complete articles and 7 abstracts are published.