In recent years, low-dimensional mixed-spin magnets have vigorously been discussed. Considering Haldane's conjecture, which proposes qualitative difference between integer- and half-integer-spin chains, what is expected for mixed-spin chains? We might begin our argument from a naive question of this kind. Mixed spin chains do not necessarily have magnetic ground states. According to the geometry of the spin alignment, the system may be disordered and massive or be ordered and massless. We here discuss the latter, that is, the 
ferrimagnetism, employing one-dimensional alternating-spin models. In contrast with the ferromagnetic and antiferromagnetic ground states 
whose magnetizations are saturated and zero, respectively, the ferrimagnetic ground states have in-between magnetizations and may therefore be excited twofoldly. The ferromagnetic excitations, 
reducing the ground-state magnetization, forms a quadratic dispersion relation, while the antiferromagnetic excitations, enhancing the 
ground-state magnetization, are gapped from the ground state. These coexistent elementary excitations are so interesting as to bring a ferromagnetic and antiferromagnetc mixed aspect into both static and 
dynamic properties of ferrimagnets.