Clara Thalmann (née Ensner; 24 September 1908 – 27 January 1987) was a Swiss journalist, athlete and militiawoman, who fought during the Spanish Civil War.

Already a sympathiser of the anti-Stalinist left, she joined the Workers' Party of Marxist Unification (POUM) and helped produce its German language broadcasts.

[17] She then turned her attention to the sectarian conflicts between various Trotskyist factions,[18] helping to establish good relations between the POUM and the Italian anti-fascist refugees, who were largely organised around the Bolshevik–Leninists.

[21] Víctor Alba and Stephen Schwartz disputed the validity of this allegation, claiming it to have been motivated by a "Trotskyist disbelief" in the agency of anarchists to act without Marxist intervention and pointing out its alignment with similar Stalinist accusations against the group.

[22] During the May Days of 1937, Clara was caught up in the fighting, finding herself on a rooftop with other members of the POUM militia, including the English journalist George Orwell.

[23] After the victory of the Republican government's forces, Thalmann and her husband attempted to flee the country by boat,[24] but they were captured and imprisoned by the Communist Party of Spain (PCE).

[27] Following the outbreak of World War II and the subsequent Nazi occupation of France, Clara mostly attempted to stay out of trouble, refusing to officially join the French Resistance due to her disappointment with the collapse of anti-fascism in Spain.

[30] The fidelity of many of the allegations made in their memoirs was challenged by Víctor Alba and Stephen Schwartz, who advised caution when reading them as a primary source.

[31] When Burnett Bolloten questioned Clara herself on her husband's allegations that "right-wing" members of the POUM had shot Trotskyists, she claimed to have had no knowledge of such executions occurring.

[3] The following year, she expressed regret for the excesses of the Red Terror in Spain, particularly disagreeing with the executions of nuns that had resulted from the outburst of violence at the beginning of the war.