This paper presents interdisciplinary research on the transformation of Polish society and the economy. A new composite Balanced Development Index (BDI) has been constructed and applied in a ‚beyond GDP’ paradigm to analyse Poland’s socio-economic development during the 1999-2014 period and to make predictions for 2015-2017. Four groups of detailed indicators-two economic ones (external and internal) and two social ones (concerning the objective and subjective current situation, and public expectations for the future)- are used to construct four middle-level indexes, which are subsequently aggregated into the general BDI index. The congruency between the four middle-level indexes is interpreted in terms of the balance relevant for future socio-economic development. The validity of the index is proven by its high correlation with the psychological conditions of society. The results indicate a less optimistic picture of development in Poland than is provided by the GDP, which has been constantly growing.