Inequalities of Rellich type

Hardy inequalities have been important topics of research for a century, and in the past twenty years or so, there has been a deluge of important papers on various versions, including discrete and fractional forms and extensions to Rellich and higher-order inequalities. This paper is a brief survey of known fractional and nonfractional forms of the Rellich inequality together with some new results and remarks concerning the Rellich inequality, including the case of the $p$-Laplacian for $p \in (2,\infty)$.