The Ocean Tensor Package is an open-source package for matrix and tensor operations on CPU and GPU. The package aims to serve as a foundational layer for applications that require dense tensor operations on a variety of device types. All operations are available through a unified interface that is carefully designed to be powerful, extensible, and at the same time easy to use. The package has a modular implementation in C and provides a light-weight Python interface. Modularity of the package facilitates the addition of new operations as well as new device types.