Q. Are women allowed to wear tallit and/or tefillin?
A. There is a general principle that women are exempt from positive commandments (“thou shalts”) which have to be fulfilled at a particular time. However, there are exceptions to this rule.
Time-bound positive commandments which are intrinsically linked to negative commands, such as Kiddush on Shabbat, which is linked to the prohibition of work on Shabbat, are obligatory on women. Time-bound positive commands which celebrate events in which the whole community was involved, such as hearing the M’gillah on Purim, are likewise obligatory on women.
There are also commands which women have chosen to observe out of piety, such as hearing the shofar.
However, the general principle still applies in relation to tallit and tefillin. Since these mitzvot involve something that is worn, authorities tend to apply to them the rule in the Torah that men and women should not wear clothing that is specific to the other (Deut. 22:5).
Rabbi Moshe Feinstein allows women to have tzitzit on any four-cornered garment, provided they do so out of genuine piety and not in order to make a statement. To avoid the problem of women wearing a men’s garment, Rav Feinstein speaks of women not putting tzitzit on exactly the same type of garment as that which men wear.
In relation to tefillin, he sees no grounds for permitting them to women because they go directly on the body and there is a problem of bodily cleanliness at certain times. Because men too cannot guarantee bodily cleanliness, the usual practice is for them to keep the tefillin on for a limited time in the morning when one is praying, and not all day.