Optogenetics, a technique that uses light to control neurons, has revolutionized neuroscience by enabling precise modulation of specific cells within complex neural tissues. This review outlines the development and application of single-component optogenetic tools, which are derived from microbial opsins. These tools allow for fast, specific excitation or inhibition of neurons in complex systems, such as freely moving mammals. The microbial opsin approach, which includes channelrhodopsins (ChR) and halorhodopsins (NpHR), has been instrumental in achieving high-temporal and cellular precision in neural control. ChR2, a blue-light-activated cation channel, and NpHR, a chloride pump, are among the most widely used optogenetic tools. These tools have been refined through genetic engineering to improve their performance, including enhanced expression, faster deactivation, and reduced desensitization. Additionally, new optogenetic tools, such as step-function opsins (SFOs) and red-shifted opsins, have been developed to enable longer-lasting and more precise control. Optogenetic tools have been applied in various model organisms, including C. elegans, flies, zebrafish, and mice, to study neural circuits, behavior, and disease mechanisms. Viral vectors and transgenic animals have been used to deliver optogenetic tools into specific neuronal populations, enabling targeted manipulation of neural activity. The integration of optogenetics with electrophysiology, calcium imaging, and two-photon microscopy has expanded the ability to study neural circuits in vivo. Overall, optogenetics has provided a powerful tool for investigating the function of neurons and neural circuits in health and disease.Optogenetics, a technique that uses light to control neurons, has revolutionized neuroscience by enabling precise modulation of specific cells within complex neural tissues. This review outlines the development and application of single-component optogenetic tools, which are derived from microbial opsins. These tools allow for fast, specific excitation or inhibition of neurons in complex systems, such as freely moving mammals. The microbial opsin approach, which includes channelrhodopsins (ChR) and halorhodopsins (NpHR), has been instrumental in achieving high-temporal and cellular precision in neural control. ChR2, a blue-light-activated cation channel, and NpHR, a chloride pump, are among the most widely used optogenetic tools. These tools have been refined through genetic engineering to improve their performance, including enhanced expression, faster deactivation, and reduced desensitization. Additionally, new optogenetic tools, such as step-function opsins (SFOs) and red-shifted opsins, have been developed to enable longer-lasting and more precise control. Optogenetic tools have been applied in various model organisms, including C. elegans, flies, zebrafish, and mice, to study neural circuits, behavior, and disease mechanisms. Viral vectors and transgenic animals have been used to deliver optogenetic tools into specific neuronal populations, enabling targeted manipulation of neural activity. The integration of optogenetics with electrophysiology, calcium imaging, and two-photon microscopy has expanded the ability to study neural circuits in vivo. Overall, optogenetics has provided a powerful tool for investigating the function of neurons and neural circuits in health and disease.