This special issue of the Journal of Mathematical Sciences (Volume 280 Number 1, 2024) is a collection of selected papers from the Workshop OTHA Spring 2023 held from 18 to 22 April 2023 in Yerevan. There were no officially appointed Guest Editors. But we are very glad that the President of the Academy of Sciences of Armenia Prof. Ashot Saghyan, Academician, Doctor of Sciences, supported this issue and provided his greeting to the participants of the issue. The Academy of Sciences of Armenia was established on November 10, 1943, and 23 well-known scientists were elected as founding academicians, including M. Abegyan, the Alikhanyan brothers, R. Acharyan, Av. Isahakyan, V. Hambartsumyan, the Orbeli brothers and others. The first president of the Academy of Sciences was an outstanding scientist, historian, and orientalist Iosif Orbeli. Since then, many great names of researchers from Armenia have been inscribed in the annals of world science thanks to their discoveries and achievements, among them there are many mathematicians who have taken their rightful place among the outstanding scientists.

This special issue of the Journal of Mathematical Sciences (Volume 271 Number 6, 2023) has been established in honor of Professor Anatoly G. Kusraev in the occasion of his 70-th birthday. Professor Kusraev is an acknowledged leader in the field of Boolean-valued analysis. He owns beautiful results in dominated operator theory, vector integration, the structure of Kaplansky-Hilbert modules, C*-modules and operator algebras, spaces with mixed norm, injective Banach lattices, and similar cyclic objects and phenomenons that were unknown previously. Guest Editor: Semen S. Kutateladze.

The special issue “Mathematical analysis and differential equations” (Volume 271 Number 5, 2023) of the Journal of Mathematical Sciences (JMS, Springer Nature) has been published following the results of the International Conference on Mathematical Analysis and Differential Equations, which was held from September 19 to 23, 2022 in Tsaghkadzor (Armenia). Regional Math Center the Southern Federal University co-organized this conference along with other centers and the Academy of Sciences of Armenia. Scientists from Armenia, Russia, Germany, Belgium, France, Portugal, and Ecuador took part in the conference. More information in the Preface by the Editor-in-Chief of JMS Alexey Karapetyants at the link: https://link.springer.com/article/10.1007/s10958-023-06654-0

This special issue of the Journal of Mathematical Sciences (Volume 266 Number 3, 2022) has been established in honour of professor Stefan Samko, Doctor of Sciences, on the occasion of his 80-th birthday. This thematic collection was preceded by the activities within the framework of the OTHA international conference in 2021 which was dedicated to the 80th anniversary of S.Samko.
Guest Editors: Alexandre Almeida (Portugal), Zalina Kusrayeva (Russia) and Humberto Rafeiro (UAE).

This special issue ((Volume 266 Number 1, 2022) of the Journal of Mathematical Sciences (Series A) has been established in honour of Professor Nikolay Karapetyants (1942-2005), Doctor of Sciences, on the occasion of 80-th anniversary from the date of his birthday. This thematic collection was preceded by the activities within the framework of the OTHA international conference in 2022 which was dedicated to Professor N.Karapetiants. This issue is the first in a series of direct submissions (Series A) launched in 2022.

This thematic collection of contributed articles has been established in honour of professor Stefan Samko, at the occasion of his 80-th birthday. The contributions provided have been written by colleagues, on the basis of an invitation through the guest editors. Each of those papers sheds some light on at least one of the many research directions which have played a role in the S.Samko scientific career. This thematic collection was preceded by the activities within the framework of the OTHA international conference in 2021 which was dedicated to the 80th anniversary of S.Samko.
Editors: Alexey Karapetyants, Vladislav Kravchenko, and Elijah Liflyand.

This is the first in the two-volume series originating from the 2020 activities within the international scientific conference "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis" (OTHA), Southern Federal University in Rostov-on-Don, Russia.
Editors: Karapetyants A., Kravchenko V.V., Liflyand E., Malonek H.R.

This is the second in the two-volume series originating from the 2020 activities within the international scientific conference "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis" (OTHA), Southern Federal University, Rostov-on-Don, Russia.
Editors: Karapetyants A., Pavlov I. V., Shiryaev A. N.

This proceedings volume gathers selected, peer-reviewed papers from the "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis IX" (OTHA 2019) conference, which was held in Rostov-on-Don, Russia, in April 2019.
Editors: Alexey Karapetyants, Vladislav Kravchenko, Elijah Liflyand

This proceedings volume gathers selected, peer-reviewed papers from the "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis VIII" (OTHA 2018) conference, which was held in Rostov-on-Don, Russia, in April 2018. Prepared in the framework of ISAAC-Springer agreement.
Editors: Alexey Karapetyants, Vladislav Kravchenko, Elijah Liflyand

These issues gather selected papers from the "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis VII" (OTHA 2017) conference, which was held in Rostov-on-Don, Russia, in April 2017.

The issue gathers selected papers from the "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis VI" (OTHA 2016) conference, which was held in Rostov-on-Don, Russia, in April 2016.

The issue gathers selected papers from the "Modern Methods, Problems and Applications of Operator Theory and Harmonic Analysis V" (OTHA 2015) conference, which was held in Rostov-on-Don, Russia, in April 2015.