This paper presents the first observation of an X-ray diffraction pattern from a single protein, *Escherichia coli* GroEL (14 nm diameter), the smallest biological sample ever imaged by X-rays. The experiment demonstrates that the 'diffraction before destruction' concept extends to single proteins, enabling the determination of the protein's approximate orientation. This achievement opens the way for ultrafast, single-molecule time-resolved studies on the femtosecond timescale.

Tomas Ekeberg, Dameli Assalaoua, Johan Bielecki, Rebecca Boll, Benedikt J. Dauer, Lutz A. Eichacker, Linda E. Franken, Davide E. Galli, Luca Geisler, Lars Gumpricht, Laura H. Günther, Janos Hajdu, Robert Hartmann, Dirk Hasse, Alexandr Ignatenko, Jayanath Koliyadu, Olena Kulyk, Ruslan Kuras, Markus Kuster, Wolfgang Lugmayr, Jannik Lübke, Adrian P. Mancuso, Tommaso Mazza, Carl Nettelblad, Yevheniy Ovcharenko, Daniel E. Rivas, Max Rose, Amit K. Samanta, Philipp Schmidt, Egor Sobolev, Nicusor Timneanu, Sergey Usenko, Daniel Westphal, Tamme Wollweber, Lena Wrobs, Paul Lorouda Xavier, Hazem Yousef, Kartik Ayyer, Henry N. Chapman, Jonas A. Sellberg, Caroll Seuring, Ivan A. Vartanyants, Jochen Küpper, Michael Meyer, Filipe R. N. C. Maia