Integration of renewable and energy storage components in standalone/grid-connected energy systems, which results in hybrid energy systems, is increasing nowadays. Optimisation of hybrid energy systems is an essential matter for economic, clean, convenient and reliable energy supply. Since the optimal design should satisfy multiple objectives, application of multi-objective optimisation is preferred rather than a single-objective solution. By multi-objective optimisation, a trade-off among different objectives can be obtained. This study presents a timely survey on the state-of-the-art in multi-objective optimal design of hybrid standalone/grid-connected energy systems. The existing literature is categorised by various indices: (i) standalone or grid-connected mode; (ii) number and type of objective functions; (iii) completely renewable-based or dieselrenewable- based hybrid systems; and (iv) multi-energy systems. The applied objective functions, design constraints and decision variables in the optimisation of hybrid energy systems are addressed. It is found that the recent objective functions like customer satisfaction and grid-dependency need further investigation in the multi-objective design procedure.