<p>The General Theory of Relativity (GR) is a reparametrization invariant and non deparametrizable theory, afflicted with the problem of time when canonically quantized. Therefore, in theories of Quantum Gravity the notion of time evolution is somewhat subtle. Over the last several decades, numerous approaches have been proposed and discussed to recover a meaningful notion of temporal evolution for such theories. These include, the identification of internal clocks, deparametrization procedures, gauge fixing methods, and extended phase-space quantization. In this short review, we will briefly discuss the development of these ideas. Focusing on deparametrization procedure we also present an analysis of a reparametrization invariant simple model and show that the problem of time for this model can be sorted out. This is done essentially by promoting one of the observables of the theory to the level of time-like parameter. Our proposed model reflects essential features of a reparametrization invariant theory like GR. Moreover, this model, which we are going to discuss, is formally non- deparametrizable but it will be shown that a sort of deparametrization can still be achieved. This deparametrization is achieved by implementing the idea of noninteracting subsystems as was proposed in Page and Wooters mechanism. This in turn renders our theory free from the problem of time. We, therefore, expect that this short review and the discussion of a simple model could serve to refresh the very interesting topic of the problem of time in quantum gravity.</p>