Sublease

• A sublease is a separate lease, made by a lessee to another party, which grants the lessee part of the term of the lessee's original lease. It is important to note, however, that a sublease by definition retains part of the original lease for the lessee. For instance, Sean has seven years left on his lease, and then subleases to Mark for five of those years. Mark is the sublessee, and Sean retains an interest known as a reversion. After the five years of Mark's sublease, the lease will revert to Sean for two more.
  
  

Assignment

• Should a lessee transfer the whole of his remaining interest under a lease to a third party, that transfer is not a sublease, but rather an assignment. In the above example, should Sean wish to entirely get out of his original lease and just give the lease to Mark for the remainder of its term, he would assign the lease to Mark and retain no interest at all. The distinction between sublease and assignment is important, because it creates different legal rights and duties for the parties involved.
  
  

Enforcing a Sublease

• In a lease, the lessor and lessee make certain promises to each other. Likewise, in a sublease, the lessee and sublessee make promises to each other. However, in a sublease (as opposed to an assignment), the sublessee can only enforce those promises made to him by the lessee in the sublease, not those promises made by the lessor in the original lease. If the lessee assigns the lease, the assignee would take on all duties and rights under the original lease, but the sublessee is bound by the terms spelled out in the new sublease.
  
  

Assumption Agreements

• Should parties wish to incorporate terms of the original lease into the sublease, they may do so using a certain type of contract known as an express assumption agreement. For instance, if Sean and his landlord agree that they want Mark to be responsible for all of Sean's promises to the landlord in the original lease, as well as all of Mark's promises to Sean in the sublease, they would have Mark sign an agreement in which he assumes all of the promises in the lease. Note that express assumption does not constitute assignment of the lease; Sean remains liable to the landlord for Mark's failure to deliver on lease promises.
  
  

Warranty of Habitability

• Although a sublessee generally can only claim the legal rights explicitly granted to him by the sublease agreement, many states impose certain legal requirements on landlords which the landlords cannot remove from the contract. The most prevalent, imposed by a majority of states, is the implied warranty of habitability. By this warranty, a residential landlord promises to tenants that the premises will be habitable, up to a standard generally defined by the local housing code. Most states that enforce the warranty of habitability have ruled that sublessees may also enforce the warranty directly against the landlord, regardless of the sublease language.