For the first time, VLBI observations of a ``Whole-Sky'' sample of radio sources at low red shift and with compact radio emission at or above the level of 1 Jy can be assembled. The sample, summarised in 
9.1 and 9.2, consists of 12 sources. 6/12 lie in the Northern Hemisphere and 6/12 lie in the Southern Hemisphere. The six Southern Hemisphere sources have been studied in this thesis for the first time.
The 12 sources can be broken down into the following sub-classes: 3/12 are associated with BL Lac type objects (PKS 1514-241, 1652+398, and 1807+698), 2/12 are associated with Seyfert galaxies (0316+413 and 0430+052), 2/12 are FR I type radio galaxies (1228+127 and PKS 1322-427), 3/12 show evidence for kpc-scale jets and lobes but cannot be easily classified as type FR I or FR II (0402+379, PKS 0521-365, and PKS 2152-699), 1/12 is an FR II type radio galaxy (PKS 0518-458), and 1/12 is a GHz Peaked-Spectrum radio source (PKS 1718-649).
This sample contains a rich diversity of radio sources and an equally rich diversity in the properties of the host galaxies. This diversity is encouraging since examples of all major classes of extragalactic radio source are present in the sample.
The ``Whole-Sky'' sample may already be able to guide our understanding in some areas. For instance, only one source in the sample, 0430+052, is an apparently superluminal source. The remaining sources in the sample which have had well measured pc-scale component motions (0316+413, 1228+127, and PKS 1322-427) have subluminal speeds, until recently conflicting with the strong one-sidedness of the pc-scale jets, which indicates a highly relativistic motion for the emitting material.
Some of this conflict has recently been resolved with the discovery of pc-scale counterjets in 0316+413 (3C84, Perseus A) and PKS 1322-427 (NGC 5128, Centaurus A). However, the work presented in chapter 5 shows that the measured speed in PKS 1322-427 is still inconsistent with the observed counterjet. For 1228+127 very high dynamic range VLBI maps reveal no counterjet, again inconsistent with the measured component speeds if those speeds are assumed to be the true speed of the jet. The often cited escape from this problem is to allow the jet to travel at a much faster speed than the components which are observed, the component speeds suggested to be pattern speeds on top of an underlying faster flow.
However, the problem may be complicated somewhat by the suggestion that large amounts of free-free absorbing material can cause apparent asymmetries in pc-scale radio sources, in addition to the effects of Doppler beaming. Evidence for significant free-free absorption on the pc-scale has been presented for two sources in the ``Whole-Sky'' sample, 0316+413 and PKS 1322-427.
These results show that the pc and sub-pc-scales in radio galaxies are extremely complicated, with the jets and their environments intimately connected. Further observations of the nearby radio galaxies offer the best opportunities for a better understanding of the conditions in the jet and its environment within a few pc of the core.
Another area where we can gain a better understanding is in the study of the GHz Peaked-Spectrum radio sources. The discovery of the lowest red shift GHz Peaked-Spectrum radio source is a very significant result from this thesis. PKS 1718-649 is at a red shift which allows highly detailed radio imaging with VLBI but more importantly high spatial resolution optical investigations. With HST resolution the inner 100 pc of the AGN could be imaged, revealing for the first time the region close to the radio source.
Models for GPS sources rely upon a confining medium to constrain the radio source to sub-galactic dimensions, implying heavy interactions between the expanding radio source and its environment. It is this interaction which may drive the strong optical emission observed for GPS sources. High spatial resolution, narrow-band optical imaging of PKS 1718-649 may allow direct tests of models for GPS sources. PKS 1718-649 is unique in this respect. Other GPS sources are too far away to allow the appropriate resolution to be achieved.
Finally, in a broader sense, VLBI observations of the nearby sources may add to our understanding in unexpected ways. For instance, the SHEVE observations of PKS 2152-699 revealed a relationship between the optical and radio structure over 4 orders of magnitude in spatial scale, from the pc-scale to the scale of tens of kpc.
Future observations of all the objects in the ``Whole-Sky'' sample will be important for our understanding of similar sources which lie at higher red shifts and hence do not allow such detailed investigations. This is perhaps where the greatest value of the ``Whole-Sky'' sample lies, in providing a list of sources to attack with observations over a wide range in wavelength and resolution. In this way we can strive to understand individual sources in detail and hence improve our understanding of the rest of the radio loud AGN population.