City Nature Challenge is an international citizen science initiative, promoted by the Natural History Museum of Los Angeles County and the California Academy of Sciences. The challenge, which aims at increasing the knowledge of urban nature through public participation, involves cities from several countries. It\u2019s a bioblitz-style competition, where cities challenge each other in gathering the highest number of observations, finding the highest number of different taxa, and engaging the highest number of citizens. As a result of the successful 2017 edition of City Nature Challenge (> 4000 people involved across 16 US cities; >125,000 observations; >8600 species) the event has gone global. In 2018, 68 cities all over the world were involved in a 4-days competition in which over 17,000 citizens have collected more than 440,000 observations of 18,000 taxa. Rome and Padua were the two Italian cities taking part in the contest. The participants used two mobile applications, \u201cCSMON-LIFE\u201d and \u201ciNaturalist\u201d. More than 250 Italian citizens collected 1,700 observations of more than 500 taxa. Data have been validated and are now feeding national (Italian Network of Biodiversity) and international (Global Biodiversity Information Facility) aggregators of primary biodiversity data. These data will be used to investigate environmental issues such as: biodiversity impact due to the presence of invasive alien species; effects of climate change; conservation of rare species; human effects on environment. The success of this global citizen science initiative paved the way for defining new strategies in biodiversity data collection to support the development of international research infrastructures, such as LifeWatch
