Languages show a restricted number of relativization strategies. Depending on the linear position in which a relativized head noun appears, relative clauses (
RC
s) are classified into
prenominal/right‐headed
,
postnominal/left‐headed
, and
in‐situ
RCs. This classification is further refined depending on the structural position of a relativized head noun: whether it is syntactically
external
to the relative clause CP or
internal
to it. The latter type are called internally headed RCs (IHRCs). Thus, there can be logically three types of IHRCs:
in‐situ
IHRCs,
left‐headed
IHRCs, and
right‐headed
IHRCs.
IHRCs are observed in a relatively small number of languages of the world, but are by no means typologically rare. They are indeed found in geographically diverse areas, across genetically unrelated languages.
An important goal from the perspective of generative grammar is to investigate the structures of IHRCs and to reveal universals and parameters that make IHRCs available in some languages but not in others. In search of them, various linguists have proposed typological generalizations that are claimed to hold of IHRCs universally, such as a word‐order generalization and a
wh‐in‐situ
generalization. However, each generalization faces limits and exceptions. This chapter examines what the studies on IHRCs have discovered so far over the years and carefully considers what universals should be extracted from them and what should be taken as parameterized. It will focus on two sides of syntax of IHRCs: the internal syntax and the external syntax. A language with an IHRC must have a syntactic mechanism available that allows a relativized head to remain internal to a relative clause but to be linked as an argument of an element external to the relative clause. The chapter will also discuss syntactic subtypes of IHRCs from a cross‐linguistic perspective.