Microneedles, first conceptualized decades ago, have gained significant research attention since the mid-1990s due to advancements in microfabrication technology. They are designed to deliver drugs, vaccines, and other bioactive substances through the skin, eye, or cells. Microneedles can be categorized into solid microneedles for skin pretreatment, drug-coated microneedles, dissolving microneedles, and hollow microneedles for drug infusion. Solid microneedles create pores in the skin to facilitate drug diffusion, while drug-coated microneedles deliver drugs directly into the skin upon insertion. Dissolving microneedles are made from water-soluble or biodegradable materials that dissolve in the skin, leaving no waste. Hollow microneedles provide a conduit for pressure-driven flow of liquid formulations or diffusion of drugs into the skin. Microneedles have been used to deliver a wide range of substances, including low molecular weight drugs, biotherapeutics, and vaccines, with applications in clinical trials and commercial products. The success of microneedles depends on their ability to facilitate insertion, skin recovery, drug stability, and patient outcomes such as pain, irritation, and infection. Microneedles are poised to advance further into clinical practice, offering improved pharmaceutical therapies, vaccination, and other applications.Microneedles, first conceptualized decades ago, have gained significant research attention since the mid-1990s due to advancements in microfabrication technology. They are designed to deliver drugs, vaccines, and other bioactive substances through the skin, eye, or cells. Microneedles can be categorized into solid microneedles for skin pretreatment, drug-coated microneedles, dissolving microneedles, and hollow microneedles for drug infusion. Solid microneedles create pores in the skin to facilitate drug diffusion, while drug-coated microneedles deliver drugs directly into the skin upon insertion. Dissolving microneedles are made from water-soluble or biodegradable materials that dissolve in the skin, leaving no waste. Hollow microneedles provide a conduit for pressure-driven flow of liquid formulations or diffusion of drugs into the skin. Microneedles have been used to deliver a wide range of substances, including low molecular weight drugs, biotherapeutics, and vaccines, with applications in clinical trials and commercial products. The success of microneedles depends on their ability to facilitate insertion, skin recovery, drug stability, and patient outcomes such as pain, irritation, and infection. Microneedles are poised to advance further into clinical practice, offering improved pharmaceutical therapies, vaccination, and other applications.