By RAW, being charmed does not end concentration; it isn't listed in the things-that-break-concentration in PHB 203. However, it would still be up to the DM, if he so rules, that a check would be needed, as PHB 204 states: > The DM might also decide that certain environmental phenomena, such as a wave crashing over you while you’re on a storm-tossed ship, require you to succeed on a DC 10 Constitution saving throw to maintain concentration on a spell. Being _charmed_ isn't an *environmental* effect, per se, but in keeping with 5e's spirit of rulings-over-rules, I think leaving it up to the DM would be how it was intended. ---------- OK, daze, but that isn't really helpful if I'm the DM ----------------------------------------------- Consider the spell being concentrated on and the charmer in question. If the spell is detrimental to the charmer, a _charmed_ person would likely end the spell as > You can end concentration at any time (no action required). (PHB 203) because, according to the rules on being _charmed_ in PHB 290: > A charmed creature can't attack the charmer or target the charmer with harmful abilities or magical effects Anything other than that, a check or ending concentration outright would be totally within the rules.