The paper is composed of three main parts: Introduction of the first part reflects the processes of gradual transformation of the human society under the influence of specialisation, that lead to continuous growth of enormous volume of specialized knowledge. Under the influence of dynamically changing societal circumstances, we are no longer capable of to control and handle this knowledge in full complexity that, in many occasions, lead us unwittingly, and dangerously, to preference of certain interests over the others. The consequences of this phenomenon is resulting not only in critical relation of man and his natural environment, but also in incremental disintegration and alienation of urban environment of our cities, that is failing to mediate interaction and synergy between various social, functional or spatial components of urban life in one place. Forces that drive development of our society materialize in our cities in specific forms of spatiality that traditional architecture is not capable to efficiently grasp. Impact of traditional architecture on formation of urban environment is constantly declining. This amplifies adverse effects on spatial, functional as well as user environment of our cities. The main objective of this paper is to draw attention to unexploited potential of specific spatial forms of contemporary city, labelled here as "host structures". The paper introduces concept of "invasive interventions" and formulates broader scope of their interpretations and understanding as of initiatory impulses for establishment of basic forms of urban life on "host structures", in aim to enrich the quality of urban space and stimulate public activities. The invasive interventions that emerge as result of coordinated expression of collective will of real users of the city, often beyond the established models of economic efficiency or profit, are of particular significance for today city. The paper illustrates number of their various appearances on actual examples. Second part of the paper is focused on introduction of methodology of evaluation and comparison of invasive or urban interventions. This methodology consists of three parts: 1) Recording of their visual or audiovisual properties. 2) Evaluation of selected universal quantitative and qualitative parameters and their visualisation in diagram. 3) Verbal description summarizing the context and specific values of selected parameters as well as of characteristic properties that universal part of evaluation is not able to capture. Application of this methodology is subsequently demonstrated on 20 examples of invasive or urban interventions. Third part of the paper represents application of "research by design" method. Application of concept of invasive interventions is demonstrated here on three examples of actual design work of author in various in contexts of the city. Further description of those examples aims to amplify understanding of general principles of invasive interventions and presents some of the actual tools of their possible implementation.