1 Introduction  
2 Abstract setting  
3 Scalar second order operators with complex coefficients  
4 The operator $\nabla^{t}(\mathcal{A}\nabla u)$  
5 The $p$-ellipticity  
6 $L^{p}$-dissipativity for operators with lower order terms  
7 Elasticity  
8 A Class of Systems of Partial Differential Operators  
9 The angle of dissipativity  
10 Maximum principles for linear elliptic equations and systems  
11 Other results  
12 The functional dissipativity  
13 Concluding remarks