The thesis by publication is expanding across countries, institutions and disciplines, and so a more in-depth understanding of the format across contexts is warranted, to ensure that all stakeholders understand the implications of this format and implement it in a fair and transparent manner. This paper provides a cross-sectional analysis of policies related to the Thesis by Publication in six countries, investigating requirements and restrictions related to the timing and number of publications, publication and authorship status, preferred publication characteristics, and structure and format of the submission, with an ultimate aim to answer the question: what makes a Thesis by Publication? The findings show diversity across programs and flexibility within them, but present a common yet broad conceptualisation that maintains the integrity of doctoral research. Less attention to finer details may reflect flexibility and autonomy but may also lead to uncertainty for doctoral researchers, supervisors, and examiners.