In ecotoxicology, the non-forced exposure approach provides a complementary perspective to traditional ecotoxicity tests by giving the organisms an opportunity to flee to adjacent, less contaminated areas, thus allowing them to escape from any toxic effects. This approach recognizes the chemical heterogeneity among connected habitats with different levels of contamination. The Heterogeneous Multi-Habitat Assay System (HeMHAS) is a non-forced aquatic assay system that allows the free movement of the organisms throughout various compartments with the possibility to select an area according to its attractiveness or aversiveness. This system expands the environmental risk assessment (ERA) by studying the habitat selection response based on the organism's ability to perceive the surrounding environment. This represents a new frontier in ERA, where different factors other than just contamination can be integrated to assess the cost-benefits balance when a habitat is selected. Thus, the HeMHAS has become a valuable habitat-selection based approach to assess the factors driving the spatial distribution of organisms in connected ecosystems with different levels of contamination. The aim of the current work is to describe the different types of HeMHAS, their ecological relevance, technical advantages and disadvantages, and to critically discuss its applicability and results that have been published in line with landscape and stress ecology.