Before a wedding it is tradition for the bride to have parties with her female friends and relatives at a bridal shower.
Traditionally, according to MarthaStewartWeddings.com, the shower was not supposed to be hosted by a relative of the bride, as it gave the impression the party was just so the bride could get gifts. Instead, it was supposed to be thrown by the bride's friends.
Now, it is acceptable – and often common – for relatives of the bride to throw the bridal shower.
It is also common now for the bride to have multiple showers. The bride might have one shower for family that's thrown by relatives, and another one for her friends that's hosted by her bridal party.
If the bridal party hosts the shower, the maid-of-honor is usually tasked with hosting and planning the shower. However, the duties can be shared amongst the entire bridal party.
If the bride-to-be is having multiple showers, the various hosts should connect with each other to make sure guests aren't being invited to multiple showers.