William John Grassie (born May 3, 1957) is an activist for numerous causes, including nonviolence and a freeze on nuclear weapons, reform of science education, and greater dialogue between science and religion. He is the Executive Director of Metanexus Institute, an organization which worked closely with the John Templeton Foundation to promote “dialogue and interactive syntheses between religion and the sciences internationally.”
Grassie was arrested in several non-violent civil disobedience actions and was a symbolic war tax resister. Grassie and David Falls, another employee of the Religious Society of Friends, a Quaker organization, refused to pay federal taxes on the grounds that it would support nuclear war, but a judge ruled, in a civil suit by the IRS in 1990, that the church was obliged to enforce levies against the salaries of the two employees.  A statement by the Friends Quaker religious organization followed:
(Grassie and Falls) are not tax evaders, but deeply religious and conscientiously motivated individuals who feel they cannot pay the military portion of their taxes without violating the central tenets of their religious faith.— Statement by the Yearly Meeting, a Quaker organization, 1990.
In 1987 and 1988, Grassie worked as a community organizer in Southwest Germantown, Philadelphia, and organized the “Three Hundred Anniversary Celebration of the Germantown Protest Against Slavery” in commemoration of the first European protest against slavery in the New World (1688). The project was designed as a community development initiative and helped catalyze a community revitalization project now known as “Freedom Square”.
The Philadelphia Center for Religions and Science was founded in 1998, and it changed its name in 2000 to the “Metanexus Institute on Religion and Science” to reflect its international reach. In 2011 the organization shortened its name to simply Metanexus Institute and is now based in New York City. The organization originally promoted dialog between religion and science, but now "promotes scientifically rigorous and philosophically open-ended explorations of foundational questions" through engagement with Big History.
- The New Sciences of Religion: Exploring Spirituality from the Outside In and Bottom Up, New York: Palgrave Macmillan, 2010.
- Politics by Other Means: Science and Religion in the 21st Century, Philadelphia: Metanexus, 2010.
- H+/-: Transhumanism and Its Critics, Philadelphia: Metanexus, 2011 (edited with Gregory Hansell).
- Advanced Methodologies in the Scientific Study of Religious and Spiritual Phenomena, Philadelphia: Metanexus 2010 (edited).
- Applied Big History: A Guide for Entrepreneurs, Investors, and Other Living Things, Mexanexus Imprints, 2018.
- WILLIAM ROBBINS, June 9, 1982, The New York Times, KROL ASSESSES POSITION IN DISARMAMENT MOVEMENT, Accessed Aug. 27, 2013, quote= ... William Grassie ... a Philadelphia Quaker .. a director of the Pennsylvania Campaign for a Nuclear Weapons Freeze...
- David O'Reilly, February 19, 1996, Philadelphia Inquirer, Looking For The Tao In Science Classrooms The Templeton Foundation Gives Grants To Colleges With Ideas. Several In The Area Were Recipients., Accessed Aug. 27, 2013, quote= ...lecturer William Grassie's portable computer can flash color images of living cells and space shots of Earth ...
- Ursula Goodenough and William Grassie, June 02, 2006, Philadelphia Inquirer, Teaching science as a rich narrative Presenting key facts that are not connected makes eyes glaze over. Try this new approach., Accessed Aug. 27, 2013, quote= ...One conclusion stands out: Ten years of reform efforts have not (yet) had a measurable impact ...
- David O'Reilly, February 18, 2002, Philadelphia Inquirer, Center thinks religion and science can say much to each other, Accessed Aug. 27, 2013, quote= ... William Grassie, Metanexus' executive director and vice president, ...
- Tom Infield, The Philadelphia Inquirer, March 26, 1982, "A New Breed is Battling Arms Race"
- William Robbins, The Windsor Star, June 12, 1982, A Cardinal's Campaign..., Accessed March 21, 2013
- Jane Eisner, The Philadelphia Inquirer, September 23, 1982, " A Drive for Support of the Nuclear Freeze."
- "William Grassie: Religious Liberties and Moral Ambiguities - The Cases of Contraception and War Resistance". Huffingtonpost.com. Retrieved 2012-10-04.
- Joseph A. Slobodzian, Philadelphia Inquirer, August 19, 1988, "IRS Sues Phila. Quakers Over Tax Protest."
- Jim Smith, December 21, 1990, Philadelphia Inquirer, , Accessed Aug. 27, 2013, quote= ... The ruling stemmed from two civil cases filed in 1988 by the IRS against the Philadelphia Yearly Meeting, the area's 13,000-member Quaker organization.
- Rich Henson, The Philadelphia Inquirer, April 24, 1988, "Germantown Parades for Justice."
- Jan Gehorsan, Associated Press, March 15, 1998, Ill-Fated Anti-Slavery Document Focus of Week's Activities, Accessed Aug. 27, 2013, quote=You could call it a failure, since slavery continued for nearly two more centuries, said the event's coordinator, William Grassie.