Sensors based on nanostructured materials, due to their extremely reduced size as well as electrical and optical properties related to the matter arrangement, are able both to communicate with the infinitely small world and to perceive and to reveal even a single molecule in the atmosphere or a single ion in the liquid. In addition the development of nanostructured sensing materials provides high surface-area-to-volume ratio layers mimicking the strong biological sensory systems. These sensors should be used when the conventional analytical equipment, although characterized by better accuracy and precision, cannot be applied for several reasons as, eg. big size, energy consumption, needs of skilled users, impervious locations, continuous monitoring over large areas, extremely toxic or dangerous environments, etc. Research activity on nanostructured sensors for pollutants monitoring for designing and fabricating nanofibrous and nanocomposite sensors, by electrospinning technology, differently functionalized for selective monitoring of pollutants (outdoor and indoor) has been supported by the European Cooperation in Science and Technology (COST Action MP1206, 2013-2017), and fit the requirements of further national and international projects. Additionally, such a research aims to miniaturize sensor devices for decreasing weight, size energy consumption and cost as well as to develop suitable platforms with hybrid sensors for the simultaneous monitoring of many environmental parameters and to improve the communication capability (wireless connectivity) among sensors. This research activity fits the challenging concept of “Citizen Observatories” of Horizon 2020 based on citizens’ own devices (e.g. smart phones, tablets, laptops, and other social media) used together with innovative technologies to strengthen environmental monitoring capabilities, have the potential to generate new and original applications to reduce investment and running costs of in-situ observations and monitoring applications and solutions.