The Italian Network for Long-Term Ecological Research (LTER-Italy) is a network of terrestrial, freshwater, transitional and marine sites, where ecological researches are carried out at multi-decadal scale by the national research institutions and universities, with the aim of investigating a large variety of ecosystems, their components and functioning. LTER-Italy (www.lteritalia.it) includes 25 sites with 79 research stations distributed throughout the Country (with sites also in the Ross Sea, Antarctica, and in Himalayan lakes) and, since 2006, is part of the LTER-Europe Network (www.lter-europe.net) and the LTER International Network (ILTER; www.ilternet.edu/). This Special Issue presents a compendium of researches carried out in a number of LTER-Italy sites. The papers report investigations performed in different ecosystems to understand their dynamics and evaluate their response to natural or anthropic forcing.