We have all seen and likely signed liability waivers before participating in a recreational activity. Skiing, trampolines, zip lines, gym memberships, equipment rental, athletic participation forms, etc. all require liability waivers before you can participate in the activity.
These waivers are generally enforceable, but not always.
The general rule is that a liability waiver is not enforceable if it violates public policy, if the negligence is one where a legal standard of care exists and the act falls well below that standard, or if the drafting of the waiver is insufficient. Last, gross negligence cannot be waived in advance.
The public policy analysis is multi-factorial, with no one thing being more important than another, but looking at the situation as a whole. The factors include whether the activity is suitable for public regulation, whether the party seeking the waiver is providing an important public service, whether the party provides the service to anyone or to certain people, whether the party seeking the waiver has control over the activity, and also whether the parties had the ability to negotiate the contract and the bargaining power of the two parties.
If a legal standard exists, such as in a landlord / tenant relationship, whereby one party already owes a legal duty to keep the other free from types of negligence, then the obliged party cannot simply draft an agreement to exonerate it should their negligent act cause future harm to the other.
A waiver is not enforceable if it is unfairly written, either because it is unclear or even if it is included as a non-descript portion of a larger document. If someone wants to exclude future liability it must be done clearly and prominently.
Last, even if the waiver is enforceable, we still must ask whether the negligence act that later occurred was one where the actor was merely negligent or whether gross negligence occurred. While a difficult thing to prove, gross negligence is that which substantially goes beyond the simple unreasonable conduct that might be deemed negligent. Put another way it is the failure to exercise even slight care.
In summary, while liability waivers are generally enforceable, they can be overcome depending upon the unique circumstances of the case, using the above analysis.