Aart Klein’s career as a photographer began in 1930 with the photo press agency Polygoon. Although he was working there initially as an office clerk, he also started doing some photography himself. During his nine years at Polygoon’s, Aart Klein grew into one of the agency’s foremost photographers. Unfortunately, the negatives of the photographs he made in that period have been lost. During the German occupation, Aart Klein held a number of small jobs as a photographer. In 1943, he was forced to do labour in Germany, where he continued working as a photographer. After a year, he obtained leave, and when he got back to the Netherlands he went into hiding. During the last year of the German occupation, Aart Klein worked for the resistance and his photographs were passed on to England.