The purpose of this paper is to establish the foundations of multimicrolocalization, in particular, to give the fiber formula for the multimicrolocalization functor and estimate of microsupport of a multimicrolocalized object. We also give some applications of these results.X}. This shows, in particular, soundness of our framework in the sense that the sharp estimate can be achieved by a geometrical tool (the multi-normal cone) already prepared in our framework. These two results have many applications, and some of them will be given in the last two sections of this paper.The paper is organized as follows: We briefly recall, in Section 1, the theory of the multi-specialization developed in [4]. Then, in Section 2, we define the multi-microlocalization functor by repeatedly applying Sato's Fourier transformation to the multi-specialization functor. After showing several basic properties of the functor, we establish a fiber formula which explic-For p = (0, 0, 0; 1, 1, 1):.When I = ∅ we obtain the functor of multi-microlocalization: Set ∧ := ∧ {1,...,ℓ} for short.where N k is R n k with coordinates x (k) = (x i ) i∈Î k . Set, for k ∈ {1, . . . , ℓ}, (2.5) J ≺k := {j ∈ {1, . . . , ℓ}, I j I k }, J ≻k := {j ∈ {1, . . . , ℓ}, I j I k }, J ∦ k := {j ∈ {1, . . . , ℓ}, I j ∩ I k = ∅}.Clearly we have (2.6) k ∈ J ≺j ⇔ I k I j ⇔ j ∈ J ≻k , and, by the conditions H1, H2 and H3, we also have (2.7) J ≺k ⊔ {k} ⊔ J ≻k ⊔ J ∦ k = {1, 2, . . . , ℓ}.