"Inferno of Choices: Poles and the Holocaust," edited by Sebastian Rejak and Elzbieta Frister - a large compilation of primary source material from the WWII era, with many items published for the first time in English
Informational link to the Aquila Polonica publishing company, which has published many books about the Polish experience in WWII
The Kreisau Project, which seeks the reconciliation of Germans, Jews and Poles through the arts
Background information about Karski and his family from Google
The book The Eagle Unbowed: Poland and the Poles in the Second World War, by Halik Kochanski paints a picture of Poland before and during the war
A review of this important book in the Commonweal Magazine
A book about the Katyn Massacre that Karski would have been killed in if he had not participated in a prisoner exchange
A thoughtful examination about Polish-Jewish relations by Filip Mazurczak, with a mention of Karski, and several useful statistics about Righteous Gentiles in the wartime era
An article by former Karski student Joshua Muravchik in Mosaic Magazine about Karski's background and impact
Information about The Mass Extermination of Jews in German Occupied Poland, a 1942 brochure that the Polish Government-in-Exile compiled, using intelligence from Karski and others, that documented ongoing Nazi atrocities during World War II