AlGaN-based materials have been recognized as one of the most promising materials for optical devices in the short-wavelength region because of the tunable direct bandgap from 3.4 to 6.2 eV by verifying the Al content from 0 to 1, as well as the thermal and chemical stability. After the two-step method was used to grow GaN-based materials, a high-quality GaN layer was obtained and several GaN-based photoelectric devices have been developed, including the GaN-based light-emitting diodes (LEDs), laser diodes (LDs), photodetectors (PDs), and so on. At present, even though GaN-based blue LEDs are available in the market, GaN-based photoelectronic devices in the deep ultraviolet (UV) region are still facing many challenges because of the relatively poor quality of AlGaN. Compared with GaN, the growth of AlGaN is more difficult due to the pre-reaction and short migration length of the Al atom. In addition, GaN buffer or substrate is not suitable for the growth of AlGaN since the strain in AlGaN will induce AlGaN to crack. Furthermore, the activation energy for Mg in AlGaN is higher than in GaN, resulting in the big problem of obtaining high-quality p-doped AlGaN, thus obstructing the application of AlGaN-based photoelectric devices. In this chapter, we will introduce the developments, challenges, and applications of AlGaN-based material and focus on the efforts that have gone into improving the quality of AlGaN.