## 1 Introduction  
In his idiosyncratic talk \"There's plenty of room at the bottom\" in 1959, [PERSON] envisioned that it should be possible to build nanoscale machines that could carry out chemical synthesis through mechanical movement [1]. He also presented [PERSON]'s idea of miniature surgical robots that could perform predefined tasks in the human body [1]. Now, almost 60 years later, thanks to modern biology, we know that the human body is actually a large-scale biofactory that is comprised of a great number of tiny and accurate nanomachines, such as motor proteins and enzymes, as a result of billions of years of evolutionary processes on Earth. However, we are not merely products of those natural nanomachines or simply hosts to them, but we are also able to look at them with our state-of-the-art microscopes, and even more interestingly, to create artificial and completely new nanodevices. In other words, we are putting [PERSON]'s idea into practice. At the time of [PERSON]'s talk, the structure of double-stranded DNA (dsDNA) was resolved just six years before [2]. However, it was known that DNA carries genetic information and how DNA strands hybridize to each other following Watson-Crick base-pairing rules [2]. Nevertheless, it took almost 30 years before the potential of DNA molecules as programmable construction materials [3]--and not merely as the storage of genetic information--was proposed by [PERSON] [4]. Since then, the field of structural DNA nanotechnology constantly grew and it started to truly flourish during the last decade [5; 6]. Today, researchers routinely use DNA to build not only static two- and three-dimensional (2D and 3D) nanostructures via self-assembly [4; 5; 6; 7; 8; 9; 10; 11], but also dynamic and precise nanodevices and robots [12; 13] that [PERSON] could hardly imagine. As a matter of fact, [PERSON]'s statement \"Biology is not simply writing information; it is doing something about it\" [1] is literally realized in the case of DNA molecules and DNA nanotechnology. Although structural DNA nanotechnology constantly evolved during the last 35 years, starting from [PERSON]'s vision of using DNA junctions and lattices to build DNA crystals [6; 7], the recently witnessed big boom in the field started from the invention of 2D DNA origami in 2006, a technique developed by [PERSON] [14]. DNA origami is based on a long single-stranded DNA (ssDNA) scaffold that is folded into a desired nanoscale shape with the help of dozens of short oligonucleotides [14]. Since 2006, the method was extended to 3D shapes [15; 16], designs with curvatures and twists [17; 18], wireframe-based and automatically designed structures [19; 20; 21], and assemblies that can reach micrometer or gigadalton scales [22; 23]. Inspired by DNA origami, scaffoldless methods that are based on brick-like assemblies were also developed [24; 25]. The benefits of using the DNA origami technique are not only the virtues of custom nanoscale shapes, but also extremely accurate molecular-scale positioning and patterning. These features can be used in controlling chemical reactions [26; 27; 28], creating tunable plasmonic systems [29; 30], and building carriers for drug delivery [12; 31; 32; 33; 34; 35]. Precise and addressable DNA origami can also be used as rulers and in optical super-resolution imaging [36], forming crystals and nanoparticle superlattices [37; 38], and creating inorganic nanostructures [39]. Recently, it was also observed that DNA origami structures are more resilient than previously understood [40], and that the mass production of DNA origami is affordable [41]. Therefore, highly versatile and modular DNA origami is about to become a standard molecular-scale tool in numerous laboratories. In this review, we discuss DNA origami nanostructures that can be used as dynamic and controllable nanodevices, such as walking robots [42], logic-gated nanopills [12], and rotors [43] (see Scheme 1).