Historical overview and introduction: discovery of cosmic radio waves, origins of radio astronomy, thermal and non-thermal radiation, radio observations and the challenge of radio frequency interference. Radiation physics: luminosity, flux, flux density, intensity, blackbody radiation, Rayleigh-Jeans approximation, brightness temperature, coherent radiation, interference, polarization, Stokes parameters. Radio telescopes: primary reflectors, beam pattern, feeds and reflector illumination, surface errors, heterodyne receivers, transmission lines, front-end and back-end receiver components; noise, noise temperature and antenna temperature; bolometer detectors, spectrometers, polarimeters, very low-frequency radio astronomy. Single-dish observations: switched observations, measuring system temperature, antenna temperature; antenna beam, main beam and angular resolution, main beam efficiency, extended sources, observing resolved and unresolved sources, spectral-line observations, radio images, calibration of radio telescopes, sensitivity. Interferometric observations: need for resolution, two-element interferometer, observing a single-point source, fringe function, visibility function, observing a pair of unresolved sources, observing a single extended source, coherence and the effects of finite bandwidth and integration time. Aperture synthesis: need for both sensitivity and resolution, cross-correlation of received signals, complex-valued cross-correlation, complex correlation of a single-point source at single frequency, extended sources and the Fourier transform, source structure and the visibility function, uv tracks, interferometers as spatial filters, sensitivity and detection limits. Interstellar medium: 21-cm spectral line of atomic hydrogen, rotation curve of the Galaxy, distribution of HI in the Milky Way, warm and cold gas, rotational lines of molecules, distribution of molecular clouds in the Galaxy, thermal emission from dust. HII regions and nebulae: HII regions, Bremsstrahlung emission from HII regions, radio recombination line emission, classification and evolution of HII regions, planetary nebulae. Radio emission from stars: solar radio emission, thermal radio emission from stars, giant and supergiant stars, flare stars, radio emission young stars and proto-stellar disks, radio pulsars, supernova remnants. Radio emission from galaxies: 21-cm HI observations, molecular gas in galaxies, radio continuum emission from galaxies, dust emission, active galactic nuclei, AGN models, radio galaxies and quasars, center of our Galaxy. Cosmic microwave background: cosmological models, blackbody nature of CMB, temperature anisotropies in CMB, polarization of CMB. HI intensity mapping: high-redshift 21-cm radiation from the intergalactic medium, dark ages and cosmic dawn, structure formation and the 21-cm signal, global 21-cm signature, intensity mapping, future of 21-cm cosmology.