Stones circles, put quite simply, are rings of standing stones, although not all of them are cicular, many being eliptical. Many have definite layout plans and often stone circles in one region share a similar style, e.g. Cork features many axial stones circles, where a recumbent stones faces an apparent entrance into the circle (see Drombeg (County Cork)).

They are the most well known of megalithic monuments and the ones most likely to capture anyone's imagination. Many theories exist about the original purpose of these enigmatic structures, the most popular (and at times most controversial) one is that they were built as astronomical observatories, many having apparent solar alignments with the sunrise and sunsets at the solstices and equinoxes. Lunar and star alignments have also ben noted.

No matter what the exact purpose it is certain that they played a significant role in the ritual or religious lives of the builders. One thing that nearly everyone has in common is that they are located in the most dramatic of places, usually offering unrivalled views.

Quite often other monuments, such as alignments, cairns, boulder burials or outliers, are to be found in close proximity to stone circles.