  Supernovae (SNe) are the most brilliant optical stellar-class explosions.
Over the past two decades, several optical transient survey projects discovered
more than $\sim 100$ so-called superluminous supernovae (SLSNe) whose peak
luminosities and radiated energy are $\gtrsim 7\times 10^{43}$ erg s$^{-1}$ and
$\gtrsim 10^{51}$ erg, at least an order of magnitude larger than that of
normal SNe. According to their optical spectra features, SLSNe have been split
into two broad categories of type I that are hydrogen-deficient and type II
that are hydrogen-rich. Investigating and determining the energy sources of
SLSNe would be of outstanding importance for understanding the stellar
evolution and explosion mechanisms. The energy sources of SLSNe can be
determined by analyzing their light curves (LCs) and spectra. The most
prevailing models accounting for the SLSN LCs are the $^{56}$Ni cascade decay
model, the magnetar spin-down model, the ejecta-CSM interaction model, and the
jet-ejecta interaction model. In this \textit{review}, we present several
energy-source models and their different combinations.
