The time Laplace‐transform domain convolution‐type reciprocity relation for acoustic waves in a fluid/solid configuration is derived. Arbitrary inhomogeneity, anisotropy, and loss mechanisms are taken into account. Reciprocity between transmitting and receiving transducers located in either the fluid or the solid parts of the configuration is established. It is shown how the reciprocity relation leads to the source‐type wave field integral representations for direct source problems and to the integral‐equation formulation of inverse source, and direct and inverse scattering problems through the associated contrast source representations. Since neither a fluid inclusion in a solid nor a solid inclusion in a fluid leads to a regular perturbation problem in the integral‐equation formulation, the embedding must be adapted to the location of the contrast sources as far as the type of medium (fluid or solid) is concerned. Applications to acoustic emission and to acoustic imaging and profile inversion are briefly indicated.