A review is given of experimental verifications of the general theory of relativity (GTR) in which basic assumptions and consequences of the theory are compared with experiment. It may now be considered that the principle of equivalence and some of the other propositions forming the foundations of GTR, and also the effects predicted by it for weak fields ($\vert\varphi\vert$/c$^2\ll1$, where $\varphi$ is the Newtonian gravitational potential) have, on the whole, been reliably confirmed. However, in the case of strong fields, the theory has not as yet been directly confirmed. In particular, the existence of black holes has not yet been demonstrated, to say nothing of a quantitative agreement between GTR formulas and measurements of the metric near a black hole. Several suggestions are put forward in relation to further verifications of GTR.