In 2008 the International Organization for Standardization (ISO) decided to put together a new expert working group ISO/TC 43/SC 1/WG 54 named “Perceptual assessment of soundscape quality”. The purpose of this expert group is to propose the first ever, international standard on how to measure the perceived quality of soundscapes, by means of questionnaire techniques. This work is chiefly motivated by a need to harmonise methods in soundscape research internationally in order to improve the comparability of research results across countries and over time. Within the Swedish research program Soundscape Support to Health, the present authors developed such a technique based on field work and laboratory studies. In the present paper we present research in which we validated our initial findings and finalised our questionnaire protocol. We propose that the measurement of perceived soundscape quality must include: (1) identification of perceived sounds sources, such as, technological sounds, human sounds, and natural sounds, (2) classification of soundscape quality on a good–bad scale, and (3) qualitative measurement of a set of eight perceived-soundscape attributes defined in a two-dimensional Pleasantness–Eventfulness measurement model.