The 'invisible asset' of human social/civic propensities; an aspect of the more general notion of human capital, defined here. This concept has recently been increasingly recognized as of great importance in the evaluation of social programs.1 Social capital is constructed out of the more general notion of individual human capital, which is the sum of the physical and intellectual abilities, skills, powers, experience, health, and attitudes a person has acquired. These blur into their-and their community's-social capital, which includes their relationships ('social networks') and their share of any latent attributes that their group acquires over and above the sum of their individual human capital. For example, the extent of the trust or altruism that pervades a group, be it family, army platoon, corporation, or other organization, is part of the value the group has acquired, a survival-related value that they (and perhaps others) benefit from having in reserve. (Example of non-additive social capital: the skills of football or other team members that only pay off for anyone when they are part of a team with complementary skills.) These forms of capital are, metaphorically, possessions or assets to be called on when needed, although they are not directly observable in their normal latent state. A commonly discussed major benefit resulting from the human capital of trust and civic literacy is support for democracy; a less obvious one, resulting in tangible assets, is the set of efforts towards a Universal Digital Library containing 'all human knowledge'. Human capital can usually be taken to include natural gifts as well as acquired ones, or those whose status is indeterminate as between these categories (e.g., creativity, patience, empathy, adaptability), but there may be contexts in which this should not be assumed. (The short term for all this might seem to be human resources but that term has been taken over to mean employees, and that is not what we are talking about here.) The above is a best effort to construct the current meaning: the 25 citations in Google for 'human capital' and the 10 for 'social capital' at 6/06 include simplified and erroneous as well as diverse uses; few dictionaries have caught up with these terms.