In some publications it is referred to as two distinct species: P. alcon on wet heathland, moist fen meadows and bogs at low altitude and P. rebeli on dry and subalpine calcareous grasslands. However, genetic research has shown that both have to be considered as being one species.

European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

In the European region, the Alcon Blue occurs across most of the continent. This species is listed as Near Threatened due to a decrease in occupancy of over 20% which has occurred in the past 10 years in Europe and the EU 27 region, and from which a population reduction of at least 20% is inferred. This assessment is based on regional expert opinion.

Within the European region, this species occurs in central Europe, from southern Scandinavia to the northern Iberian Peninsula and the Apennines in Italy, and from France eastwards to Romania, the Balkans, Belarus, Ukraine and European Russia. It is found at altitudes between sea level and 2,200 m.

In the EU 27 region, this species' area of occupancy is 6,064 km² and the extent of occurrence is 3,753,194 km².

The global range of this species extends across the Palearctic through Siberia to Mongolia. The global distribution area of the species is situated both within and outside Europe.

Although widely distributed in its European range, this species always occurs in local, isolated populations and is restricted to good quality (semi-) natural habitats. Declines in distribution or population have been reported in several countries. It is classed as Critically Endangered in Andorra (although regional experts now believe it is extinct), Belgium, Croatia, Czechia, Estonia; and Endangered in Belarus, Germany, Lithuania, Netherlands, Poland, Slovenia, Slovakia, Switzerland, Sweden (Maes et al. 2019). It is also classed as Vulnerable in Albania, Austria, Denmark, Hungary, Italy, Romania, Ukraine; and Near Threatened in Bosnia and Herzegovina, France, Greece, North Macedonia and Spain.

Regional experts report this species is declining in part of its distribution. In the Netherlands Phengaris alcon alcon has declined from over 130 populations to just 15 and in Belgium the butterfly was hardly recorded in 2022 and may even be extinct. The Alcon Blue is also reported to be declining in France (outside protected areas), Slovenia, Romania but declining more slowly in Germany and is stable in Czechia. In Switzerland this species is also declining strongly but there are more stable populations in the foothills of the Swiss Alps. In Italy, P. alcon alcon is declining with only five severely fragmented localities remaining; on the other hand P. alcon rebeli is widespread, although there have been many extinctions as habitat is lost to afforestation (S. Bonelli, G. Dusej, Z. Fric, X. Houard, Z. Kolev, D. Maes, M. Musche, L. Rakosy, C. van Swaay and R. Verovnik pers. comm.). A population reduction of at least 20% in the past 10 years is inferred from an occupancy decline of over 20%.

The Alcon Blue occurs in local, scattered populations, on low-lying wet heathland, on moist fen meadows and bogs and on dry calcareous grasslands. In some publications it is referred to as two distinct species: P. alcon alcon on wet heathland, moist fen meadows and bogs at low altitude and P. alcon rebeli on dry and subalpine calcareous grasslands. However, genetic research has shown that both have to be considered as being one species. The bright, white eggs are easy to find. They are laid on the flowers and sepals of Marsh Gentian (Gentiana pneumonanthe) or Willow Gentian (G. asclepiadea) in the case of the wet habitat P. alcon alcon, and on Cross Gentian (G. cruciata) by the dry habitat P. alcon rebeli. At first, the small caterpillars feed on the ovaries of the foodplant, but they pass the later instars in the nests of various Myrmica ants, M. ruginodis, M. scabrinodis and sometimes M. rubra. They hibernate and pupate in the ant nests. The Alcon Blue has one generation a year.

Habitats of the subspecies alcon, adapted to wet localities: humid grasslands and tall herb communities (30%), mesophile grasslands (9%), broad-leaved deciduous forests (9%), heath and scrub (9%), fens, transition mires and springs (7%).
Habitats of the subspecies rebeli, adapted to dry localities: dry calcareous grasslands and steppes (50%), alpine and subalpine grasslands (33%), dry siliceous grasslands (11%), mesophile grasslands (5%) (van Swaay et al. 2006).

Phengaris alcon rebeli is threatened by a lack of suitable grassland habitat management (both agricultural intensification, such as land drainage, and abandonment). Fragmentation and isolation of habitat is the most important threat to P. alcon alcon on heathlands, although the species can survive for a long time in small habitat patches. In north-western Europe (the Netherlands, Belgium), it is also threatened in nature reserves by habitat degradation of wet heathlands, caused by large-scale lowering of groundwater table and by nutrient input. In Italy, drought has led to late-flowering of the hostplant about a month later than the butterfly's flight period. In Bulgaria, the butterfly is threatened by urban development.

All butterflies are collected to some extent, but only for the extremely rare species can it be a problem and the trade in Europe is generally at a low level compared to other continents. There is no specific trade information for this species.

This species occurs in a number of protected areas across its range. In countries where the species is declining, suitable habitats should be protected and appropriately managed to prevent the loss or degradation of wet heathland, overgrazing, and/or scrub and tree invasion of grasslands by hydrological control or by maintaining or restoring traditional low intensity agricultural grazing practices. The effects of conservation actions should be monitored by butterfly monitoring schemes. Egg counts have proven to be a very effective monitoring technique and are possible on most sites with a small time-investment.