Abstract. Motivated by two recent works of Micu and Zuazua and Cabanillas, De Menezes andZuazua, we study the null controllability of the heat equation in unbounded domains, typically R+ or R N . Considering an unbounded and disconnected control region of the form ω := ∪nωn, we prove two null controllability results: under some technical assumption on the control parts ωn, we prove that every initial datum in some weighted L 2 space can be controlled to zero by usual control functions, and every initial datum in L 2 (Ω) can be controlled to zero using control functions in a weighted L 2 space. At last we give several examples in which the control region has a finite measure and our null controllability results apply.Mathematics Subject Classification. 35K05, 93B05, 93B07.