From brain slice to freely moving mouse, optical methods are being used to probe single neuron physiology and neural circuit function. Efforts in physics, engineering, and genetics have resulted in novel techniques that permit more refined optical interrogation of brain function. The field of optogenetics has enabled neural activity to be driven by light, while optical read-out of neural activity has been improved in terms of speed, spatial resolution, and imaging depth. Genetically encoded sensors and activators of neural activity can now be expressed in cell subtypes helping us to understand neural circuits with unprecedented detail and specificity. In this chapter, we discuss some of the currently available optical methods while highlighting their relative strengths and weaknesses.