The anisotropic poroelastic constitutive model is reexamined in this article. The assumptions and conclusions of previous works, i.e., Thompson and Willis and Cheng, are compared and clarified. The micromechanics of poroelasticity is discussed by dividing the medium into connected fluid part and solid skeleton part. The latter includes, in turn, solid part and, possibly, disconnected fluid part, i.e., fluid islands; therefore, the solid skeleton part is inhomogeneous. The constitutive model is complicated both in the whole medium and in the solid skeleton because of their inhomogeneity, but the formulations are simplified successfully by introducing a new material constant which is defined differently by Cheng and by Thompson and Willis. All the unmeasurable micromechanical material constants are lumped together in this constant. Four levels of assumptions used in poroelasticity are demonstrated, and with the least assumptions, the constitutive model is formulated. The number of independent material constants is discussed, and the procedures in laboratory tests to obtain the constants are suggested.