Non-invasive neuromodulation, including the application of transcranial direct current (tDCS), alternating current (tACS) and random noise (tRNS) stimulation, provides researchers and health care professionals with the ability to gain ultimate insight into brain functions and, mainly using tDCS, to treat several neurological and psychiatric conditions. Indeed, the number of published research and clinical studies on this field is exponentially increasing. However, in parallel, several methodological, scientific, social and ethical caveats have emerged that deserve closer examination by those who would like to continue the usage of this methodology in the future. One of the main problems is related to the non-replicability of many previously published research findings, others include the rapid proliferation of the off-label applications, over-the-counter and do-it-yourself device usage, without a full understanding of safety and efficacy implications. Indeed, more work is required to understand mechanisms underlying the effects of transcranial stimulation in health and disease and also substrates of inter-individual variability in order to optimize dosing and methodological designs and safety aspects. Furthermore, related to future clinical applications, different regulatory paths for the devices, professional conduct, training, should be better regulated nationally and internationally.