The EOM-CC family of methods is based on the Fock-space parameterization of the wave-function. EOM-CC is a multi-state approach in which different manifolds of target states are described by choosing a particular combination of a reference state and a general excitation operator. General excitation operators in single-reference theories are defined with respect to the reference state, which defines the separation of the occupied and virtual orbital spaces; they can include only creation (i.e., particle) operators corresponding to the virtual orbitals and annihilation (i.e., hole) operators corresponding to the occupied orbitals. The In the EOM-CC formalism, different manifolds of target states are described by combining a particular reference state and a particular type of excitation operator (orbitals occupied in the reference state are marked by red dashed boxes). For example, electronically excited states are described by particle-and spin-conserving excitations from (usually) a closed-shell reference corresponding to the ground state, giving rise to the EOM-EE-CC method. Cationic or neutral doublet states can be described by ionizing operators acting on a closed-shell reference, giving rise to EOM-IP. Doubly ionizing operators can be used to access diradical-type or doubly ionized states (EOM-DIP). In a similar fashion, electron attaching operators acting on a closed-shell reference provide access to anionic or neutral doublet states (EOM-EA). Double electron attaching operators provide access to diradical states or to a subset of excited states derived from excitation from HOMO (EOM-DEA). By using high-spin references and spin-flipping operators, other types of multi-configurational states can be described (EOM-SF, EOM-DSF). Note that in EOM-IP and EOM-DIP, the principal character of target states is described by the hole operators acting in the occupied orbital space (red boxes), whereas in EOM-EA and EOM-DEA it is described by the particle operators acting in the virtual space. In EOM-EE, the EOM operators act in both spaces.