What's the difference between assigning a lease and subleasing it?

The two are often confused because they solve a similar problem — space you no longer need, or a lease you want out of — but they work very differently. With an assignment, the incoming tenant steps fully into your shoes; once it completes, the landlord looks to the new tenant for rent and performance, not you (subject to the lease wording — some leases keep the outgoing tenant liable as guarantor). With a subleasing, you remain on the hook: if your subtenant stops paying, the landlord still comes to you.

Most commercial and industrial leases require the landlord's consent to either, and that consent typically can't be unreasonably withheld — but the landlord will want to satisfy itself on the incoming party's covenant strength before agreeing. Practical differences follow from there: assignment is cleaner if you want a full, final exit; subleasing suits a temporary surplus of space, such as a business that has downsized but expects to grow back into it.

Whichever route fits, start the conversation with the landlord early. A landlord who understands your reasons and sees a credible incoming tenant or subtenant will usually work with you — a long-term owner's interest is in a well-occupied, well-maintained building, not in making an exit difficult.