From The Lead at Episcopal Café:
Starting Advent 1, clergy of the Diocese of Massachusetts are being given leave by Bishop Thomas Shaw to solemnize same-gender marriages for eligible couples.
In a letter posted to the blog Telling Secrets, Bishop Shaw clarifies:
Solemnization, in accordance with Massachusetts law, includes hearing the declaration of consent, pronouncing the marriage and signing the marriage certificate. This provision for generous pastoral response is an allowance and not a requirement; any member of the clergy may decline to solemnize any marriage.
Massachusetts clergy are not permitted to use the Prayer Book (in which marriage is described as “the union of husband and wife”), but, in keeping with resolution C056 from this summer’s General Convention, are instead encouraged to use other liturgical resources. (That same legislation called on “bishops, particularly those in dioceses within civil jurisdictions where same-gender marriage, civil unions, or domestic partnerships are legal, [to] provide generous pastoral response to meet the needs of members.”)
Otherwise it’s business as usual for clergy navigating rules for officiating at marriage services: Shaw notes, “We request that our clergy follow as they ordinarily would the other canonical requirements for marriage and remarriage.”
