Genetically modified (GM) mosquitoes are an important tool in the fight against mosquito-borne disease, both indirectly through their use in research investigating host–pathogen interaction, mosquito olfaction, and anthropomorphic behavior and in future direct uses for suppression and possibly eradication through sterile insect technique (SIT) and/or gene-drive programs. Successful creation of GM mosquitoes depends on microinjection procedures that precisely deliver injection materials while causing as little damage to mosquito embryos as possible. Genetic modification reagents, such as transposon system components (vector plasmids, helper plasmids, and helper mRNA), and CRISPR–Cas9 components (guide RNAs, Cas9 protein, plasmids expressing Cas9 and/or guide RNAs, and donor plasmids used in homology-directed repair [HDR]), must be delivered into the preblastoderm embryo at the posterior end where the pole cells will form before cellularization occurs. Sharp needles that pierce the embryo easily are important tools in this procedure and work best when the embryos are not desiccated. The two main procedures for mosquito embryo microinjection involve injecting embryos under halocarbon oil or under aqueous solution.