  In the first of a series of three lectures we discuss ways of measuring the
power available to feed the jets in powerful FR II radio sources. For
unobscured radio-loud QSOs we present evidence that this power is directly
related to the UV-optical luminosity, or probably more accurately, to the power
radiated through processes of accretion in a strong gravitational potential. It
has been suggested on theoretical grounds that powerful radio jets are a
necessary component of the central engine. It then follows, from the similarity
of the optical-UV power output, spectral energy distribution, and emission-line
spectra of radio-loud and radio-quiet QSOs, that radio-quiet QSOs have the same
power available to feed jets as do radio-loud QSOs. This then leaves us with
the puzzle of why we do not see the powerful jets in radio-quiet QSOs.
