As a new member of the two-dimensional transition metal dichalcogenides, platinum diselenide (PtSe₂) has attracted increased attention due to its exciting electronic and optical properties, especially its layer-dependent transition between semiconductor and semimetal: Type-II Dirac fermions. These excellent properties enable applications in various areas such as thin film transistors, broadband photodetectors, sensors, and catalysts. In this chapter, we will introduce the basic properties of PtSe₂, the current synthesis strategy of two-dimensional PtSe₂, and its nanoelectronic, optoelectronic, sensor, and catalytic applications.