Macroinvertebrates have been used for aquatic environmental bioassessment in Thailand on the Ping River system, Northern Thailand, since 1990 by applying the BMWP score procedure originally developed in the UK. However, the score has been adapted to BMWPTHAI because of different taxa, different tolerances to pollution, and taxonomic difficulties. Biomonitoring and bioassessment have been applied in many contexts such as using adults of Trichoptera species as bioindicators for streams and rivers, studies of the impact of agricultural pesticides to enzyme activities in aquatic insects, development of rapid bioassessment protocols using benthic macroinvertebrates for evaluating river health, and a study of the accumulation of microplastics in some aquatic insect species. Recently, we have been developing some taxonomic keys of aquatic insect groups, such as pictorial keys of adult Trichoptera from Southeast Asia, mayfly larvae in Thailand, and Simulidae larvae of Thailand. New taxonomic keys for macroinvertebrates are needed for biomomitoring and bioassessment for streams and rivers in Thailand because the animals in this area are unique. Currently, we are preparing a pictorial key of the caddisflies from the Mekong River and its tributaries (in Myanmar, Laos, Thailand, Cambodia, and Vietnam). Information on species distribution will be provided with the pictorial key.