To mark the 25th Anniversary of the Polish Society of Ecological Engineering (PTIE) and the 15th Anniversary of the journal “Inżynieria Ekologiczna - Ecological Engineering” it was decided to come back with the contribution on „Essence and tasks of ecological engineering” first published in the proceedings of scientific seminar on „Engineering of agricultural environment” held in Lublin 1996, as well as to report on the most significant achievements of the PTIE and the conclusions resulting therefrom. Ecological engineering encompasses both theoretical and applied knowledge covering many fields of science and technology which provide fundamentals for a wise use and protection of the natural environment and anthropogenic resources. Ecological engineering supports environmental aspects of civilization development. The basics of ecological engineering are the oldest (next to medicine) fields of science and technology.