Isogeometric analysis (IGA), which directly uses CAD models for analysis, is one of the most active research topics in both computational mechanics and computer-aided geometric design. The rapidly growing interests in IGA has led to profound developments of relevant theories and applications, among which is structural design optimization. The advantages of using IGA in structural optimization lies mainly in three aspects: (i) the integration between CAD and FE models averts the manual transition efforts; (ii) the high-order continuity of basis function enhances sensitivity analysis; and (iii) the ease of mesh refinements enriches the design flexibilities by controlling design variables. 

However, there are barriers limiting the development of IGA and IGA-based design optimization. First, as many CAD parameterization methods are not analysis-suitable, it is essential to develop general and powerful parameterization methods that are not only capable of describing complex geometries, but also analysis-suitable. Meanwhile, structural design optimization based on such parameterization methods needs to be investigated to make the best use of the developments. Secondly, as CAD modeling tools are intensively involved in IGA, the numerical implementations of IGA-based studies can be less accessible for researchers with a background of mechanics. Hence, works with detailed numerical implementations, preferably with software codes for benchmark problems, should be highly valued. Last but not least, as most of the studies have been demonstrated to solve simple benchmark problems, studies for potential engineering applications or complex geometries should be encouraged. 

With the rapid growth of researches in IGA, we initiate this special issue to highlight the recent developments, challenges and opportunities of IGA and IGA-based structural design optimization, with particular focus on theory developments, numerical implementations and potential applications. 

Topics of interest include but are not restricted to: 
1. Isogeometric analysis and analysis-suitable parameterization methods
2. Isogeometric shape optimization
3. Isogeometric topology optimization
4. Multiscale isogeometric structural optimization
5. Automatic model generation for isogeometric analysis
6. Isogeometric analysis for complex problems
7. High-efficient isogeometric analysis/isogeometric structural optimization
8. Engineering applications using isogeometric analysis/isogeometric structural optimization
9. Numerical implementations and software codes