  The basic physics of bulk magnetic superconductors (MS) related to the
problem of the coexistence of singlet superconductivity (SC) and magnetic order
is reviewed. The interplay between exchange (EX) and electromagnetic (EM)
interaction is discussed and argued that the singlet SC and uniform
ferromagnetic (F) order practically never coexist. In case of their mutual
coexistence the F order is modified into a domain-like or spiral structure
depending on magnetic anisotropy. It turns out that this situation is realized
in several superconductors such as $ErRh_{4}B_{4}$, $HoMo_{6}S_{8}$,
$HoMo_{6}Se_{8}$ with electronic and in $AuIn_{2}$ with nuclear magnetic order.
The later problem is also discussed here.
  The coexistence of SC and antiferromagnetism is more favorable than with the
modified F order. Very interesting physics is realized in systems with SC and
weak-ferromagnetism which results in an very reach phase diagram.
  The properties of magnetic superconductors in magnetic field are very
peculiar, especially near the (ferro)magnetic transition temperature where the
upper critical field becomes smaller than the thermodynamical critical field.
  The extremely interesting physics of Josephson junctions based on MS with
spiral magnetic order is also discussed. The existence of the triplet pairing
amplitude $F_{\uparrow \uparrow}$ ($F_{\downarrow \downarrow}$) in MS with
rotating magnetization (the effect recently rediscovered in SFS junctions)
gives rise to the so called $\pi $-contact. Furthermore, the interplay of the
superconducting and magnetic phase in such a contact renders possibilities for
a new type of coupled Josephson-qubits.
