Forget paper tickets for multiple rides. You can still buy them in machines near bus and tram stops and in metro and rail stations, where multiple-ride tickets are available for 5 or 10 rides. An estimated 200,000 travellers are still using them, but they are requested to make the switch to the present digital MOBIB system. The sooner, the better, although you still have some time left to use up the present paper tickets.
The MIVB will remove validating machines from its trams, metros and buses by the end of 2016, but don't wait that long. Tickets for 5 or 10 rides will no longer be on sale as from 1 July, so you should have the switch by then. Digital MOBIB cards cost 5 euros, but some 200,000 will be distributed for free in a first phase, for those that can present a multiple-ride paper ticket.
Tickets allowing 1 ride, day passes and Airport Line tickets will still be on sale. Their format will change into a digital version at the end of 2016.