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In comparison to the agricultural industry, the number of insecticides available for public health use is relatively small. Contact insecticides, which primarily function through absorption upon contact, play a crucial role in controlling vectors that transmit infectious diseases. These insecticides, when incorporated into long-lasting insecticidal bed nets, have reduced malaria incidence by 50% in sub-Saharan Africa, where the disease affects over 260 million people annually. The widespread use of insecticides has led to declining efficacy due to insecticide resistance and negative environmental impacts, however. This thesis aims to describe how contact insecticides may be characterized and engineered for use in their most efficacious solid form. It presents the characterization of seven new crystallographic forms of six contact insecticides, significantly expanding the existing structural knowledge. A formulation containing amorphous deltamethrin is also introduced, which effectively overcomes insecticide resistance. The study of amorphous deltamethrin reveals at least two distinct forms: one that is less mobile and more ordered, resembling a glass-like structure, and another that is more mobile and fluid-like. Additionally, using a model compound, this research shows polymorphic diversity on the surface of mosquito nets and demonstrates how a metastable form of an insecticide can be generated on the net's surface. The thesis also provides evidence that the lethality of insecticides is influenced not only by their solid form but also by the substrate on which they are applied. Ultimately, the goal of this thesis is to underscore the importance of solid-state chemistry and engineering in the study and formulation of contact insecticides for the control of infectious diseases.