This PhD thesis focuses on the following three research problems in environmental monitoring and aims at contributing to progress in this research field: 1. Scale dependence of indicators, 2. Reference unit of indicators, 3. Applicability of indicators. 1. Scale dependence of indicators: In an Italian case study, the scaling effects on a correlation between stream macro-invertebrate species richness and human population size have been analysed. The results reveal that a positive correlation observed at a coarser scale turns into a negative one at finer scales. The outcomes underline once more the significance of scales of analysis in ecology. 2. Reference unit of indicators: A new reference unit for sustainability indicators has been developed for the European Alps. The potential treeline is placed at the upper limit of this reference unit, with the aim of improving the reliability of indicator results in mountain areas. The treeline has been defined by a GIS- and statistics-based approach using land-cover data and a DEM. Its validity has been verified at regional level. 3. Applicability of indicators: In order to enhance the applicability of indicators, a regional typology based on spatial-pattern indicators was carried out for the Alpine space using multivariate analysis methods. A set of 25 indicators, 5 components and 6 clusters was calculated for 17,504 municipalities, containing valuable information at different spatial levels. Evidence suggests that in the future environmental monitoring will gain in importance due to global change, population growth, species decline and climate change. Innovative solutions containing a balance between science, policy and society will be needed in order to achieve effective environmental monitoring.