Prenuptial agreements are becoming more and more common when planning for marriage due to their practicality beginning to outweigh their former "unromantic" stigma. There are many reasons to complete a prenup prior to marriage: inheritance expectations, avoidance of contentious divorces, protection of future earnings, protection of interest in family businesses, and much more.
Common provisions to include in a prenup typically begin with covering where the property acquired before and during marriage will go in the event of divorce. This includes percentage divisions. Next, a standard prenup will cover what alimony should be due and for what period. Finally, prenups will commonly cover the rights of parties' vis-à-vis each other in the event of death. An example of this would be asking the spouse to waive the right to take an elective share (a share a spouse is entitled to of their spouse's assets upon death).
Unenforceable provisions include anything pertaining to custody and child support. Determinations for custody and child support are based on the best interests of the child and parents cannot contract away the rights of their children to support. Additionally, there can be no provisions seeking to regulate the behaviors of a spouse.
Pennsylvania has specific requirements for prenuptial agreements. First, there must be full and fair disclosure (unless waived). Next the prenup must be voluntary and there can be no signs or evidence of duress when it is created. Finally, courts will not look into whether an agreement is fair and reasonable. In the view of the courts, the individuals who drafted and consented to a prenup had full control over its creation and thus must live with the provisions therein.