The concept of left-behind places or regions has skyrocketed in recent years and various empirical studies are using the concept to describe (not only) economically lagging regions. Yet, there is still no settled definition and method of measurement of left-behindness in the social sciences. In the methodological part this working paper presents a plausible conceptualisation and operationalisation of left-behind regions in European Union countries. The operationalization of “left-behindness” is guided by several principles: it is relative to national standards, multidimensional, and both structural and dynamic. Labour market regions are identified as the appropriate spatial unit for analysis. The study uses NUTS3 regions, aggregated for metropolitan areas and adjacent regions, excluding extraterritorial and small countries. A total of 918 regions across 25 countries are analysed using indicators related to economic viability, social structure, and population development from 1993 to 2021. Our empirical analysis highlights how the nature of “left-behindness” varies across Europe, with a particular focus on Central and Eastern Europe. In these regions, left-behindness is closely tied to regional disadvantages, char-acterized by low economic prosperity, reduced social status, and higher poverty rates. These areas often experi-ence stagnation or shrinkage, with non-metropolitan regions being particularly affected, possibly due to poorer infrastructure. In other parts of Europe, the different dimensions of left-behindness are less coherently associ-ated and do not form clear spatial patterns. In particular, poverty is spatially decoupled from low economic pros-perity in many countries. Overall, we identified macro-regional differences of left-behindness manifestation across Europe, shaped by historical, economic, and social factors unique to each region.