The number of studies on insecticides, which constitute an important class of pesticides, is increasing day by day. These chemicals used in the fight against pests in the field of agriculture; It is also used to fight mosquitoes and insects in homes, gardens and rural areas. Excessive use of insecticides has adversely affected many beneficial organisms besides target organisms. As a result of the negative effects of insecticides on non-target organisms, the normal balance of nature has been disturbed and this has led to the decline of some living species in the world. In many studies from the past to the present, it has been shown that these insecticides have negative effects on the environment, human and animal health. Some of these chemicals, which have many benefits in the fight against agricultural pests, have been banned due to their harmful effects on non-target organisms as a result of excessive use. Today, however, these chemicals are still used intensively against agricultural pests, threatening non-target organisms and human health. For this reason, in this book chapter we have prepared, the negative effects of insecticides on living things are examined by reviewing biochemical and histopathological studies.