Tomasz Stefan Arciszewski (Polish pronunciation: ['t?ma? art??i'??fsk?i]; 4 November 1877 – 20 November 1955) was a Polish socialist politician, a member of the Polish Socialist Party and the 31st Prime Minister of Poland, 3rd Prime Minister of the Polish government-in-exile in London from 1944 to 1947, presiding over the period when the government lost the recognition of the Western powers.