Demand and deliver: Micelles reversibly crosslinked by boronate esters (see scheme) show in vitro and in vivo stability, and thus minimize premature drug release under physiological conditions. After reaching the tumor sites, drug (stars in scheme) release is activated by cleavage of the boronate esters by the acidic conditions around the tumor or in the target cells, or by the administration of mannitol. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.