Securities in a cash account can't be lent out by the broker without the written agreement of the customer. The necessary language could theoretically be put into the standard account agreement, so if you care you should read it. However, it is not common business practice to include that in retail customer account agreements. Also, the broker is required to notify you whenever your shares are borrowed, and this requirement cannot be waived by the agreement. So if you haven't been notified about lending activity, your broker is not lending your shares. The same requirements hold for fully paid securities held in a margin account, so even if you have a margin account, if you're not actually borrowing money from them, they're not lending your shares without your knowledge.