The use of language mechanisms to enforce protection boundaries around software modules has become increasingly attractive. This paper examines the advantages and disadvantages of language-based protection over more traditional protection mechanisms, such as standard virtual memory protection hardware, software fault isolation, and capability systems. Arguably, state-of-the-art language-based protection is more flexible and as safe as these other mechanisms. Two major remaining issues are the performance of language-based protection, and the management of resources. Regarding the latter, techniques to build an operating system kernel capable of managing resources and revoking rights are presented.