  In this article, we review the status of the calculation of nuclear currents
within chiral effective field theory. After formal discussion of the unitary
transformation technique and its application to nuclear currents we will give
all available expressions for vector, axial-vector currents. Vector and
axial-vector currents will be discussed up to order $Q$ with leading-order
contribution starting at order $Q^{-3}$. Pseudoscalar and scalar currents will
be discussed up to order $Q^0$ with leading-order contribution starting at
order $Q^{-4}$. This is a complete set of expressions in
next-to-next-to-next-to-leading-order (N$^3$LO) analysis for nuclear scalar,
pseudoscalar, vector and axial-vector current operators. Differences between
vector and axial-vector currents calculated via transfer-matrix inversion and
unitary transformation techniques are discussed. The importance of consistent
regularization is an additional point which is emphasized: lack of consistent
regularization of axial-vector current operators is shown to lead to a
violation of the chiral symmetry in the chiral limit at order $Q$. For this
reason, a hybrid approach at order $Q$, discussed in various publications, is
non-applicable. To respect the chiral symmetry the same regularization
procedure needs to be used in the construction of nuclear forces and current
operators. Although full expressions of consistently regularized current
operators are not yet available an isoscalar part of the electromagnetic charge
operator up to order $Q$ has a very simple form and can be easily regularized
in a consistent way. As an application, we review our recent high accuracy
calculation of the deuteron charge form factor with a quantified error
estimate.
