In creating a legal agenda in service of the Precautionary Principle, the idea of precaution requires more inventories and better monitoring of the condition of public and workforce health than at present. Rectifying problems of the past to better serve the aims of precaution will require more affirmative pre-market and much more post-market knowledge-generation by those who create and use potentially toxic substances, improved pre-market review of substances, better responses to early warnings, and quicker protective post-market responses to evidence of toxicity. This paper conceptualizes a model pre-market screening law to highlight the need for primary prevention measures and to provide philosophic ideas for improving post-market laws and addressing a large universe of existing substances that have been poorly characterized. Although retrospective personal injury law does not have good mechanisms for precaution, even this can be more protective than it is at present by enhancing causes of action for reasonable fear of disease and medical monitoring, and moving to create new causes of action for failure to develop and disseminate information needed to assess the toxicity of substances.