Trekking permits are no longer required for most areas, including all the standard routes in the Annapurna, Everest and Langtang/Helambu/Gosainkund areas. You will, however, need to register for a TIMS card – a kind of trekkers’ register – and pay a national park or conservation area entry fee. Organized treks will do this for you.
Before setting off on any trek, register with your embassy in Kathmandu, as this will speed things up should you need rescuing. You can have KEEP or the Himalayan Rescue Association forward the details to your embassy.