Halsted had exhausted all of the medical training opportunities the United States had to offer in his position, for there was no program to train recent medical school graduates for a career in medicine at this time. Halsted then went to Europe to study under the tutelage of several prominent surgeons and scientists, including Edoardo Bassini, Ernst von Bergmann, Theodor Billroth, Heinrich Braun, Hans Chiari, Friedrich von Esmarch, Albert von Kölliker, Jan Mikulicz-Radecki, Max Schede, Adolph Stöhr, Richard von Volkmann, Anton Wölfler, Emil Zuckerkandl. He became especially close to Anton Woelfler among others which gave him unlimited access to resources. The relationships Halsted forged with these future leaders in their fields would last a lifetime. During this time in Europe, cancer was just starting to be studied more widely, making the timing of his arrival ideal. This experience inspired him with multiple new medical ideas and practices that he would contribute to in the United States.