In this chapter, we examine the stability of plasma configurations based on a magnetohydrodynamic description. This is particularly important for a wide range of configurations, since, in the pursuit of stability, the first step is to rule out rapid instability mechanisms that occur on the global magnetohydrodynamic scale. We begin by developing a general stability criterion, which takes the form of a variational principle. In the subsequent sections, we apply this principle to various configurations as illustrative examples. We start with simple pinch configurations, then, after discussing general aspects of interchange instabilities, we conclude with resistive instabilities as the final example to be addressed.iesvariational principleMHD stabilitypinch dischargeinterchange instabilityresistive instability to be discussed.