The enforceability of the convenants in a lease after an assignment, whether by the landlord or the tenant or both, is a matter of considerable practical importance. In the case of long leases, assignments of the leasehold estate and of the reversion are a common occurrence; both will often change hands many times before the end of the term, creating a welter of potential parties to any action on the covenants. In addition, there may be sureties who have undertaken to guarantee performance of the tenant's covenants. The basic principles governing the parties' rights and liabilities in this field under the present law are well known, centring upon privity of contract, privity of estate and upon statutory rules found in ss 141 and 142 of the Law of Property Act 1925. The area is one of vital commercial significance to landlords, and which potentially affects the residential security and amenity enjoyed by tenants (in the case, for example, of landlords' covenants to renew or to repair). It is also a field in which many of the issues and concepts have been the subject of judicial and academic consideration for more than a century, yet a surprising number of uncertainties remain. The law consists of a complex set of rules, which together form something resembling an intellectual jigsaw puzzle, and one from which several pieces are still missing. The aim of the first part of this article is to highlight some of these gaps.