There are many tour operators in El Calafate and El Chalten that offer all types of tours and excursions within the Parque Nacional Los Glaciares.

In Calafate
Andes Expeditions on Libertador 1341 offers day trips to Bosque Petriifcado La Leona. Tel: +54 (0) 2902 492075.
Chalten Travel on Avenida del Libertador 1174 offers tours to the glaciers as well as to nearby estancias and other activity-related excursions. Tel: +54 (0) 2902 49 2212.
Calafate Fishing on 9 de Julio 29 arranges fly-fishing trips. Tel: +54 (0) 2902 493311.
Cerro Frias on Espora 159 organises horse-riding and trekking trips on Estancia Alice. Tel: +54 (0) 2902 492808. 
Cruceros Mar Patag based in Buenos Aires offers a two-day trip aboard the Leal to glaciers Upsala, Spegazzinni and Perito Moreno.
Estancia Cristina on 9 de Julio 69 runs boat trips to the Upsala glaciar befote heading to the isolated estancia. Tel: +54 (0) 2902 491133.
Hielo y Aventura on Avenida del Libertador also offers boat excursions to Perito Moreno. Some include glacier trekking where it supplies the crampons and ice axes.
Leutz Turismo on Avenida del Libertador 1341 runs excursions to nearby estancias and Lago Roca. Tel: +54 (0) 2902 492316.
Mil Outdoor Adventure on Avenida del Libertador 1029 offers 4WD excursions. Tel: +54 (0) 2902 491437.
Mundo Austral on Avenida del Libertador 1114 has a range of tours to the various glaciers. Tel: +54 (0) 2902 492365.
Lago San Martin on Avenida del Libertador 1215 arranges excursions to local estancias. Tel: +54 (0) 2902  492858.
Patagonia Backpackers is part of the Hostels del Glaciar on Pioneros 251 or Avenida del Libertador 587 offers a glacier tour packed with information about the surrounding landscape. Tel: +54 (0) 2902 491243.
Rumbo Sur on Libertador 960 runs glaciar tours. Tel: +54 (0) 2902 492155.
Rene Fernandez Campbell on Avenida del Libertador 867 operates catamaran and launches to Perito Moreno and the Upsala glaciers. Tel: +54 (0) 2902 491298.

In El Chalten
Fitzroy Expediciones on Lionel Terray 212 organizes some excellent trekking, glacier and rock climbing expeditions. Tel: +54 (0) 2962 493017.
NYCA Aventura on Cabo Garcia 122 arranges trekking and glacier walking. Tel: +54 (0) 2962 493045.
Patagonia Aventura runs boat trips across Lago Viedma to see the Viedma Glacier. Tel: +54 (0) 2962 493110. 
Viviendo Montanas on Avenida Guemes 68 organises treks and ice climbing adventures. Tel: +54 (0) 2962 493068.
Los Glaciares Fishing in Buenos Aires arranges half-day and full-day fishing trips.