Following the Nazi occupation of much of Europe, millions of ordinary citizens found themselves cast in unfamiliar, sometimes wholly clandestine roles. Many of these roles came to be life- and death-defining. For Jews and other targeted minorities, going undercover became a matter of everyday resistance and survival. In what were previously spaces of co-existence, they routinely risked being attacked, blackmailed or exposed—at times by former neighbours or by people offering shelter. For Jews in hiding or seeking to 'pass' openly under another identity, the breakdown of all norms turned habitual, daily acts—including of self-presentation and self-orientation—into what the sociologist Stanisław Ossowski called an 'endless surviving', a 'temporary eternity'. The unbounding of past experience drove a radical reshaping of agency among people struggling to survive. According to many of their first-hand testimonies, this adaptive agency was largely defined by performance. Their recollections offer distinctive performance vernaculars that detail the covert ways of being that emerged in this world of pervasive observation and threat. This article draws on the postwar concept of Alltagsgeschichte—'everyday history' or 'microhistory' from below—to analyse a range of sources relating to occupied Poland. It investigates accounts of performing, improvising and cultivating know-how in extreme circumstances—from Jewish children masquerading as non-Jewish adults to Jewish activists passing within the Polish underground. It examines practices of self-presentation articulated by Jews living undercover, including how they interpreted changing modalities of space and unfamiliar cultural repertoires. It traces how they adapted by means of performance not only to abrupt, catastrophic situational shifts, but to changes that unfolded over years, forcing individuals to keep improvising, keep repeating—without missteps—even as conditions deteriorated beyond recognition. Finally, it suggests the everyday histories of Jewish passers constitute a cultural remembering that is increasingly vital today, as others fleeing contemporary atrocities are compelled to perform to attain refuge. [ABSTRACT FROM AUTHOR]