diff --git a/Documentation/ProjectFile/linear_solver/c_linear_solver.md b/Documentation/ProjectFile/linear_solver/c_linear_solver.md
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..2421001b7de105ef51cf5db89ec0a636d0f37a25 100644
--- a/Documentation/ProjectFile/linear_solver/c_linear_solver.md
+++ b/Documentation/ProjectFile/linear_solver/c_linear_solver.md
@@ -0,0 +1,6 @@
+In this group the configuration of linear solvers is described.
+
+Unlike all other options, there can be configurations for linear solvers from
+the Eigen, LIS, PETSc, etc. libraries at the same time. Which solver will be
+applied in the end is determined by the build configuration of the OGS
+executable.
diff --git a/Documentation/ProjectFile/linear_solver/eigen/i_eigen.md b/Documentation/ProjectFile/linear_solver/eigen/i_eigen.md
index 576add64edccf5d980a0ff86143dc43a7109a788..dae5722ba942db73637d85cb38da193cd8d8e0dd 100644
--- a/Documentation/ProjectFile/linear_solver/eigen/i_eigen.md
+++ b/Documentation/ProjectFile/linear_solver/eigen/i_eigen.md
@@ -1 +1,3 @@
-\ogs_missing_documentation
+Configuration for solvers from the Eigen library.
+
+For details see also the [documentation of the Eigen library](https://eigen.tuxfamily.org/dox/group__Sparse__Reference.html).
diff --git a/Documentation/ProjectFile/linear_solver/eigen/t_error_tolerance.md b/Documentation/ProjectFile/linear_solver/eigen/t_error_tolerance.md
index 576add64edccf5d980a0ff86143dc43a7109a788..a04ed05818f6e2cc8a6ec74741f0f429c4f1ab91 100644
--- a/Documentation/ProjectFile/linear_solver/eigen/t_error_tolerance.md
+++ b/Documentation/ProjectFile/linear_solver/eigen/t_error_tolerance.md
@@ -1 +1,5 @@
-\ogs_missing_documentation
+The tolerance of the linear solver.
+
+This setting is only applied if an iterative solver is chosen.
+
+Its default values is \f$10^{-16}\f$.
diff --git a/Documentation/ProjectFile/linear_solver/eigen/t_max_iteration_step.md b/Documentation/ProjectFile/linear_solver/eigen/t_max_iteration_step.md
index 576add64edccf5d980a0ff86143dc43a7109a788..bf4f34849e6b42c8297a9ca276bc8cb66f2bbfb0 100644
--- a/Documentation/ProjectFile/linear_solver/eigen/t_max_iteration_step.md
+++ b/Documentation/ProjectFile/linear_solver/eigen/t_max_iteration_step.md
@@ -1 +1,5 @@
-\ogs_missing_documentation
+Defines the maximum number of iterations of the iterative solver.
+
+This setting is ignored if a direct solver is chosen.
+
+Its default value is \f$10^6\f$.
diff --git a/Documentation/ProjectFile/linear_solver/eigen/t_precon_type.md b/Documentation/ProjectFile/linear_solver/eigen/t_precon_type.md
index 576add64edccf5d980a0ff86143dc43a7109a788..4a19a2c9fe9ecda78ac8b3e2d65604af79e57db1 100644
--- a/Documentation/ProjectFile/linear_solver/eigen/t_precon_type.md
+++ b/Documentation/ProjectFile/linear_solver/eigen/t_precon_type.md
@@ -1 +1,7 @@
-\ogs_missing_documentation
+Chooses a specific preconditioner for the iterative linear solver.
+
+This setting is ignored if a direct solver is selected.
+
+Possible values are NONE, DIAGONAL and ILUT.
+
+The default is NONE.
diff --git a/Documentation/ProjectFile/linear_solver/eigen/t_solver_type.md b/Documentation/ProjectFile/linear_solver/eigen/t_solver_type.md
index 576add64edccf5d980a0ff86143dc43a7109a788..47d836f7c3723ad065f2d71a160f552dae535da5 100644
--- a/Documentation/ProjectFile/linear_solver/eigen/t_solver_type.md
+++ b/Documentation/ProjectFile/linear_solver/eigen/t_solver_type.md
@@ -1 +1,5 @@
-\ogs_missing_documentation
+Chooses a specific linear solver.
+
+Possible values are CG, BiCGSTAB, and SparseLU.
+
+The default is SparseLU.
diff --git a/Documentation/ProjectFile/linear_solver/petsc/i_petsc.md b/Documentation/ProjectFile/linear_solver/petsc/i_petsc.md
index 576add64edccf5d980a0ff86143dc43a7109a788..d140d41ce7ff839cc1b0fb0fbca084207e62c1cd 100644
--- a/Documentation/ProjectFile/linear_solver/petsc/i_petsc.md
+++ b/Documentation/ProjectFile/linear_solver/petsc/i_petsc.md
@@ -1 +1,4 @@
-\ogs_missing_documentation
+Configures options for linear solvers from the PETSc library.
+
+For further details see also the
+[documentation of the PETSc library](http://www.mcs.anl.gov/petsc/documentation/)
diff --git a/Documentation/ProjectFile/linear_solver/petsc/t_parameters.md b/Documentation/ProjectFile/linear_solver/petsc/t_parameters.md
index 576add64edccf5d980a0ff86143dc43a7109a788..816c46eb4695293150803e4314d82ce93ec79e9a 100644
--- a/Documentation/ProjectFile/linear_solver/petsc/t_parameters.md
+++ b/Documentation/ProjectFile/linear_solver/petsc/t_parameters.md
@@ -1 +1,8 @@
-\ogs_missing_documentation
+Sets PETSc options from the given parameter string.
+
+The default value is <tt>"-ksp_type cg -pc_type bjacobi -ksp_rtol 1e-16 -ksp_max_it 10000"</tt>
+
+\attention
+PETSc can also receive options from the commandline arguments. However, the
+values from the prj file are applied directly to the linear solver. If
+specifying both, make sure that you check which options take precedence.
diff --git a/Documentation/ProjectFile/linear_solver/petsc/t_prefix.md b/Documentation/ProjectFile/linear_solver/petsc/t_prefix.md
index 576add64edccf5d980a0ff86143dc43a7109a788..3b980ae43308b466fce8270e8eaa0ba0c47a1f8b 100644
--- a/Documentation/ProjectFile/linear_solver/petsc/t_prefix.md
+++ b/Documentation/ProjectFile/linear_solver/petsc/t_prefix.md
@@ -1 +1,3 @@
-\ogs_missing_documentation
+Sets the options prefix for this PETSc linear solver.
+
+Cf. the PETSc [KSPSetOptionsPrefix documentation](http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetOptionsPrefix.html).
diff --git a/Documentation/ProjectFile/linear_solver/t_lis.md b/Documentation/ProjectFile/linear_solver/t_lis.md
index 576add64edccf5d980a0ff86143dc43a7109a788..f5fa016fbc09165c3e4245948dfb07e5dc65bd22 100644
--- a/Documentation/ProjectFile/linear_solver/t_lis.md
+++ b/Documentation/ProjectFile/linear_solver/t_lis.md
@@ -1 +1,11 @@
-\ogs_missing_documentation
+Defines an option string that will be passed to solvers of the LIS library.
+
+The default is <tt>-initx_zeros 0</tt>, i.e., not to overwrite the passed initial
+guess with zeroes. All other options are appended to this default value.
+
+\attention
+LIS can also receive options from the commandline arguments. However, the values
+from the prj file are applied directly to the linear solver. If specifying both,
+make sure that you check which options take precedence.
+
+Refer to the [documentation of LIS](http://www.ssisc.org/lis/index.en.html) for further details.
diff --git a/Documentation/ProjectFile/linear_solver/t_name.md b/Documentation/ProjectFile/linear_solver/t_name.md
index 576add64edccf5d980a0ff86143dc43a7109a788..fe6b18dc8b32671869a297960c260409f44c8015 100644
--- a/Documentation/ProjectFile/linear_solver/t_name.md
+++ b/Documentation/ProjectFile/linear_solver/t_name.md
@@ -1 +1,3 @@
-\ogs_missing_documentation
+Name of the linear solver.
+
+Used, e.g., to reference it in the nonlinear solver configuation.