Invited review at "Galaxies and their Masks", celebrating Ken Freeman's 70-th birthday, Sossusvlei, Namibia, April 2010. To be published by Springer, New York, editors D.L. Block, K.C. Freeman, & I. Puerari.
astro-ph/1005.0506

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Abstract. Secular evolution gradually shapes galaxies by internal processes, in contrast to early cosmological evolution which is more rapid. An important driver of secular evolution is the flow of gas from the disk into the central regions, often under the influence of a bar. In this paper, we review several new observational results on bars and nuclear rings in galaxies. They show that these components are intimately linked to each other, and to the properties of their host galaxy. We briefly discuss how upcoming observations, e.g., imaging from the Spitzer Survey of Stellar Structure in Galaxies (S⁴G), will lead to significant further advances in this area of research.

Table of Contents

• INTRODUCTION
• BARS
• Basic properties of bars
• Bar dust lanes
• Bars and spirals
• Bars and secular evolution
• RINGS
• FUTURE WORK: THE S⁴G SURVEY
• CONCLUSIONS
• REFERENCES